I have the same problem.
my phone works perfectly on T Mobile, it’s the model a1687 so it should have worked with Verizon but it doesn’t.
when you turn on the phone or after switching airplane mode on and off its says “searching” then it shows “Verizon” for a few seconds with no bars and then “no service till the end of times”
After doing some research I found out the problem, and it’s that Apple sucks in every conceivable way