Why when someone is added to a FaceTime call my phone immediately hangs up.

I recently got an iPhone 15 and nothing’s been working out for me on iMessage or FaceTime. On iMessage I’m not getting the option to do FaceTime audio calls and I’m not able to join any group calls. If I’m on a FaceTime call with someone and they add another person my phone hangs up on its own. Can someone help me?