Why do my iMessage settings keep changing on my iPhone 16?

My Imessage and facetime settings keep changing. My messages constantly go green and end up texting via apple id and my facetime started calling via apple id. In order to fix the issue i have to power off my phone, manually change the setting, and power off my phone again. Mind you it is an Iphone 16. What is going on??

[Re-Titled by Moderator]