No service

See if this Apple support article applies to your phone→iPhone 7 Repair Program for "No Service" Issues - Apple Support

If it doesn’t see this→If you see No Service or Searching on your iPhone or iPad - Apple Support

Yes, Best Buy should be able to deal with it.

If it is covered by the repair program it should be free. If the 2nd link fixes it that would also be free. If it is any other hardware failure the cost of repair by Apple would be more than the almost 5 year old phone is worth.