My iPhone 7 has been searching for signal for four days. I took it into a Verizon store, and the employee got the phone back on the network long enough to do a software update. Then, a half-hour later, it was searching again. I read somewhere I needed to take out and replace SIM card- did that, and it worked for about an hour. Does anyone know how I can permanently fix this problem? Thank you in advance for any help.