iMessage and facetime activation failure after iOS 26 update

I have an iPhone 13, and after I updated my phone to iOS 26, I cannot get my iMessage or FaceTime to work. Whenever I turn on iMessage or FaceTime, it will stay on for a second, and then it turns itself back off again. I tried to contact Apple from my iPhone, and the message kept saying failed to deliver. I got through to Apple on my Mac, and they called me, and they said they didn't know what was wrong, and they told me they would call me back, but they never did. I attempted to fix the problem myself after looking up solutions, so I tried: resetting network settings, signing out of iMessage and FaceTime, and signing out of iCloud. I actually got it to work for a little bit, but then it stopped working, and the next day. iMessage and FaceTime work on my iPad and MacBook, just not on my phone. And sometimes, if my phone decides it wants to be nice, it will sometimes let me FaceTime this one specific person, but only directly from the FaceTime app. If I click on their contact, it won't let me. I'm not sure what to do anymore to fix this issues, and it is extremely annoying and inconvenient, and I just want it to be fixed.