"No Service" message with my iphone 5

I have a 32GB iPhone 5 running iOS 10.3.3 and served by Verizon Wireless. Prior to this month, my iPhone 5 worked fine and showed 3 bars of connectivity to wifi. Then all of a sudden it showed "No Service" even though I was connected to a wifi network. The local Verizon store said there was no connectivity and that I would have to purchase a new (or used) phone. I bought another iPhone 5 online and it worked for about 2 weeks. Now it, too, shows "No Service." Again I went to the Verizon store and heard the same thing, that the Apple iPhone is malfunctioning and that the problem is not with verizon. So, what can I do other than buying another iPhone??