Frozen XR iPhone

Then you didn’t follow the instructions correctly, and you weren’t holding the SIDE button long enough:

• Press and quickly release VOLUME UP
• Press and quickly release VOLUME DOWN
• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears HOLD UNTIL YOU SEE THE APPLE LOGO, NO MATTER HOW LONG THAT TAKES.

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky.

The carrier has nothing to do with it, that’s why they couldn’t solve it. Here is the next thing to try:

If your device has iOS 15.2 or later installed, you can reset it without a computer; check out this link→How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support. Otherwise you will need a computer:

See this Apple support link→If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Or watch this companion video ⬇️

After restoring the phone using one of the methods above you can restore your most recent backup.

And if that doesn’t resolve it your phone has a hardware problem.

Follow these instructions→If your iPhone, iPad, or iPod touch won't turn on or is frozen