Question [Q] HTC ONE errors

My HTC One phone is coming up with different sorts of errors. Never been rooted or anything and a factory reset has not helped either. It was working fine previously.

Now when i try to dial out i get the error message:

Connection problem or invalid MMI code.

I also notice that it says USSD code running when i dial a number at times.

There is also a small message that says out of service area when trying to dial numbers.