Losing coverage in specific cities only
I'm on a prepaid $50/month bring your own device plan. My number is registered in Detroit and works amazingly while I'm in the city or suburbs. However, I get no reception when I go to specific cities. Over the past few months I've had this problem in Toledo, Omaha, Peoria, and Phoenix. As soon I reach the vicinity of a bigger city, the reception comes back and works perfectly again. So far I've found it to work in Detroit, Miami, San Jose, Chicago and Philadelphia.
I've tried restarting multiple times, gone to the AT&T store who put me on a call to customer care. They tried to get my phone to latch onto the network from their end, with my phone switched off, which didn't help, neither did changing the sim. So they essentially told me they don't know what's wrong and can't help me. I bought a T-mobile sim, which works in all cities, so it can't be a problem with my phone (atleast I think so). I'd rather stay with AT&T because the download speed is better when it does work. I do have to travel a lot in the next few months and this would make it a very difficult experience.
Has anyone faced a similar issue or have any idea whats going on/how to prevent this from happening?
TL;DR : No reception in mid- to low-tier cities. No improvement despite help from customer support and updating the sim. Thoughts anyone?