I have been dealing with this issue for 2 months now as well. I have been through 3 replacement phones from Verizon all work OK for a week or so then they drop network service. On all phones I have temporarily gotten service back by reseting network setting, hard reset of phone, let the battery drain to 0% and recharge, restore from back up in tunes, factory reset of phone and restore from backuP, etc, etc, etc.
I have researched the the model 1660A IPhone 7’s have a glitch that needs to be fixed by apple. So it is my understand that you have to send your phone to apple, or go to an apple store and have them give you a loaner phone while they send yours to get repaired.
My guess as to what has caused this is the latest software update to IOS 12.whatever. This IOS is designed to mess with your phone to cause you many paiful hours of tech support, waiting on hold, and no real explanation or easy resolution, except to pay over $1100.00 for apple latest phone, which will be obsolete the moment it touches your hand. I was an Android user for years, the company I work for supplies me with a work phone which unfortunately is an Iphone, so my 2 month journey of replacement phones, dropped calls, missed calls, in and out cell service because of an update that you are pestered to do, has been even more of a thorn in my side because i am not the account holder.
So .. Retsulj and everyone else with this issue. Take your Iphone smash it into a million piece mail it back to apple and go buy a new phone.