Group chats adding number in during RCS/SMS messaging, new iPhone.

I got a new iPhone 17 pro max, and I have only ever had iPhones. I noticed that all my group texts, usually with Samsung/RCS/SMS messaging, my own phone number as added at another member. I have tried removing my number, deleting the messages, starting a new thread, but text will come in from someone in the group and my number will be added again. How do I stop the madness.