Why can't I make or receive calls?

[gaudin85]

can't make or receive calls

I have a AT&T HTC one, and I put a T-mobile SIM card. It worked well.
But then, I decided I would rather switch to AT&T, got an AT&T SIM card and my numbered transferred.
Now everything works except the calls... My text messages , data network with 4G LTE, signal is at max most of the time, everything is fine...
The problem is that I soon as I want to call, the phone is stuck on "dialing" and then it hangs up... I cannot receive calls, my phone does not ring or anything when someone tries to call me. However, I send and receive text message with this same phone number and phone without any difficulty.
I know it comes from the phone, as it works well if I put my SIM card into another phone.
I tried EVERYTHING including full rebooting, calling AT&T assistance for almost 2 hrs...
Please help me !

 

[Rukbat]

Re: can't make or receive calls

Go to your nearest AT&T store. The sales associate probably can't help you (although a few of them are quite knowledgeable technically), so you might have to take the phone to a Device Support center - which the sales associate can give you the location of. (It could just be a matter of their resetting your account on their computer, though.)

 

[gaudin85]

Re: can't make or receive calls

I live 2 hrs from the closest center...