My mother's iPhone for some reason the calls not on her contacts go straight to voicemail and she gets no notification that a call comes in. She has an iPhone 13 Pro and the iOS version is 16.1.1.

So far we have checked all the settings and made sure it wasn't on silent or had the focus on. We also made sure she had a ringtone set up on it. We've done countless google searches and tried everything we can find and still doesn't seem to fix it. Normally something like this won't be a problem but she's had doctors and repair men try to contact her and the calls don't go through.

Any help with this problem would be greatly appreciated.

Update: Going to try to backup the phone and do a factory reset as suggested by someone. I'll post an update in case someone else is having the same issue.