iphone 4s sudden permanent loss of signal?

My new phone has been working brilliantly for 5 weeks, I have suddenly lost signal and cannot make or recieve calls despite fitting new sim card.I have been without phone signal for five days now. After some research it seems a common problem. Any answers out there?

Phone shows carrier name but no bars, have reset network, then full phone reset. Also switched 3g off. Still no joy😕