Phone stopped working no calls or internet, what could the problem be?

[AC Question]

Phone stopped working no calls or internet

Over 2 weeks ago my Samsung Galaxy S6 Edge phone would not connect to the internet or allow me to make calls other than emergency calls. It was bought outright and unlocked for all networks. I am with 3 and my sim works in my partners phone and his does not work in mine. The phone shows full bars at the top when the sim is in but is not working.
Samsung have taken it away twice and have returned it for the same problem to still be present.
Any ideas on what the problem is?

 

[B. Diddy]

Welcome to Android Central! If you go to Settings>Mobile Networks>Network Operators, is the proper network selected? Have you checked to make sure the APN settings are correct?

Does this happen in Safe Mode, or after a factory reset?