I have had repetitive problems with my cellular service. I commonly get a message "No Service" when I'm in a solid service area. I also get an occasional message "Cellular Update Failed". I took my iPhone 7 to the Verizon Store. They said there has been a common problem of late. They said I had two options. Upgrade to the iPhone XR for $27/month or use my insurance and get a recertified iPhone 7 for $150.
Sadly, Verizon personnel did not inform me of the best option. Take it to Best Buy or the iPhone Store and have it fixed for free. Realize that only some iPhone 7 models qualify for the free repair, but mine did. Had I not taken the time to come home and research the problem on my own, I would not have found this option and would have been out $150 or $650 with an upgrade. Beware.
Here is the Apple reference: iPhone 7 Repair Program for "No Service" Issues - Apple Support
Here is Verizon referencing the problem even though their service people did not know of this: Apple Article - No Service: Apple iPhone 7 | Verizon Wireless