Who should I contact about service in a specific location?

My wife and I have a small business and do a lot of local events.  We were at an event this weekend and had no network connection.  My Apple 11 Pro said that I had 5g with two bars, but I could not access the internet at all.  I restarted my phone multiple times as well as turning off wifi, putting it into Airplane mode and a couple other troubleshooting ideas.  Because we could not get internet, we could not connect our Square and therefore could not take any credit card sales.  Because of the lack of service I estimate we lost $200-$300 in sales.  We had alternate pay options, but most people were trying to use their credit/debt cards (which we could not).  I tried reconnecting throughout the day without any luck.  We heard other people say similar things.  The consensus from other vendors was that if you had Verizon it worked, but if you had AT&T, you were out of luck.    Fyi, this was a suburban downtown location, so it was not like we were in a field in the middle of no where.