Why does my phone say searching or no service

About a month ago my phone stopped receiving service from verizon. I can no longer get or give calls, txt messages or use the internet unless connected to Wifi. I have restored to factory settings, rebooted several times and nothing has really worked. However every now and then I am able to turn the phone off and on and it starts to work again. Im being thrown in loops as to what is wrong with my phone. I would appreciate any help or ideas on this issue.