No service

My phone comes up "no service" where the bars for the signal are. This was solved when I connected with wi-fi, while plugged in, and "updated" the phone. It happened again, a week later, and worked fine after another update. Now my iPhone 7 says "no service" again, but it is fully updated to 14.8.1. I'm sure this is some sort of "planned obsolescence" to get me to upgrade from a perfectly fine phone for my needs. Help!