AT&T Prepaid / GoPhone: trouble w/ voice calls. Deprioritized?

For the last 4 weeks we've not been able to make or receive calls using our AT&T Prepaid service in the house. If you keep dialing after about 6-10 times you can get through. The signal is fine. It's just in this neighborhood though. 1/2 mile away, no problem. It's also worse during waking hours.

My thought was: A) there are cell tower issues or B) the area is overloaded and we are getting bumped in favor of post-paid folks.

The service is generally fine and I don't want to pay $20 more for post-paid.

Has this every happened to anyone? What is the likelihood it is a priority issue vs. "bad tower" issue? I know they rebranded but I assumed there weren't any network changes.