Still getting messages despite being removed from a group. How to stop it. SECURITY ISSUE.

It sounds like you are using SMS/MMS messaging since you referred to including a device other than Apple. With any SMS messaging, these are managed by your cell provider. Apple manages group messaging with iMessage, but that is only the case when they are all Apple devices:

• You can only remove someone if the group has four or more people, and everyone is using an Apple device, like an iPhone or iPad.
• You can only add someone to a group message if they're using an Apple device. If you want to add someone to a group message but they're using a non-Apple device, you need to create a new group message. That message will use SMS/MMS by default since someone is using a non-Apple device.

Add and remove people in group text messages on your iPhone or iPad - Apple Support

As with any Support call to Apple, they will log an issue and it is not unusual for them to say there is no timeline for a fix if there is not one that would resolve the issue currently being tested in beta. I am not entirely sure Apple could provide a fix for any SMS issue and would recommend also contacting your cell provider. It is the cell provider that is sending that message to you and they are also the one's that manage the group SMS/MMS messages.

I do see that in iOS 18 Apple removed the separate Group Messaging toggle and now just uses the MMS Messaging toggle. It is actually at Settings > Apps > Messages > MMS Messaging. That includes Group Messaging and sending photos using SMS. RCS Messaging is the improved version of SMS offered by non-Apple devices, but similar to iMessage, all participants would have to be capable of RCS messaging, otherwise it would fall back to the poor experience using SMS/MMS if MMS is enabled.

More information about the difference in iMessage, SMS, RCS is available here and makes it clear the SMS/MMS is a carrier provided service. All incoming messages do appear gray like you see whether you are part of the group or not, it would just be when you send a message the green bubble would indicate if it is SMS/RCS and as always a blue bubble would be using iMessage and only communicating with Apple devices.

What is the difference between iMessage, RCS, and SMS/MMS? - Apple Support

The same problem leaving group messages happens on Android phones as well when using SMS/MMS. I included this Support Article from the Google Support forum, which explains that there is no way to remove yourself from the SMS/MMS group chat. That only solution offered is to have the entire group abandon the chat and start a new one without you. It seems ridiculous and that is why Apple created their own iMessage platform, but it is not compatible with Android. For Android it does say you can mark the chat as SPAM to stop the Notifications, so for that problem you are having, I will investigate it further how that can be accomplished on your iPhone, but that still does not remove them from the Group Chat and the texts will continue to come in just without the Notification. For now I would suggest shutting off MMS Messaging as suggested earlier and see if that stops the Notifications.

https://support.google.com/voice/thread/194120132/how-to-remove-myself-from-group-someone-else-created?hl=en

This article does a pretty good job of explaining the differences when using iMessage groups chats and those that become SMS group chats when a non-Apple device is part of the group. Once a non-apple device is added, the message bubbles will be green to signify that you are now using the SMS protocol and also the limitations of the carrier protocol for messaging, including not being able to remove yourself. The best you can do is Mute the conversation, but as you have found, there is not way to know if another person has muted the conversation, so they may still be reading those messages. This is how the group SMS messaging has always worked and is not specific to your iPhone using SMS/MMS. That is one of the benefits of using iMessage group chats with Apple devices only where you can leave the chat.

https://www.spikenow.com/blog/tips-tricks/how-to-leave-a-group-chat-on-iphone/

You can turn off Group Messaging on your device to prevent a group chat involving a non-Apple device. Just go to Settings > Messaging > Group Messaging and turn it off. This only affects messaging with non-Apple devices.

Sdjjsd wrote:

I feel like Apple has been a step ahead of me in cutting off my escape routes with every update haha.  It would be great if we had a “delete as spam” option such as Android users have.  Yeah I don’t think I should I should have to ask everyone to start a new group without me. 

To be clear, on Android it is does not delete the group chat when marked as Spam and all user still get those messages. They are just moved to a Spam folder and Notifications are stopped. There are 2 issues and the original post of being concerned about users still getting the messages in a SMS/MMS group chat as a security issue is still the case for Android and they can view what others have said at any time, the conversation is just in their Spam folder. To clarify the 2 issues:

• With both platforms, all users can still get the group chat SMS/MMS messages and the only way to exit the group chat completely is when the entire chat has been disbanded.
• The Notifications of those messages is the other issue, and you should be able to do that on your iPhone, just as can be done on Android.

Refer to the MMS sections here on the options available for both platforms and it appears they both do the exact same thing by being able to Mute further messages with the same limitation in MMS of not being able to leave the group.

• On an iPhone, visit the group chat and tap the conversation controls. Instead of seeing Leave this conversation, you will see the option to Delete and Block this conversation. If you'd rather just mute the conversation instead of deleting and blocking it, you can hit Hide Alerts to mute it.

https://www.cnet.com/tech/mobile/how-to-leave-group-chats-on-iphone-or-android-shut-off-the-noise/

Here's the kicker: SMS/MMS groups don't give you the option to leave since you're not actually using an instant messaging platform. Instead, these messages go through your carrier. So, all you can do is mute the thread or delete and block the conversation.

https://www.makeuseof.com/cant-leave-a-group-chat-on-in-apple-messages-what-to-do-instead/

There is no doubt the SMS/MMS group chats is a disaster and it has always been that way. The limitations were addressed in RCS and iMessage, so now both platforms can successfully leave group chats. You can now also use RCS on your iPhone for group chats with non-Apple devices, but similar to iMessage, all devices must support RCS Messaging, otherwise they will be using MMS if you have that option turned on. I think you will find that turning that off will eliminate that issue for you in the future. The drawback is that you won't be able to join a group chat when another device is not supporting the other messaging standards, but I don't think you want to do that anyway.

I am sure you have researched this as well and if there is any additional information Apple provides with your call that helps the situation, please update what you find out.

Sdjjsd wrote:

Awakened and annoyed, I turned off RCS messaging as well as iMessage and silenced the phone.  I hope I can still receive important work and personal messages. 

That will stop all messages including the important work and personal messages. Turning off RCS and iMessage will not stop a SMS/MMS messages, but refer to my previous post about muting these notifications instead..