I assume this has to do with the 3G switchoff.
I noticed on Friday that I cannot make or receive calls.
The phone is on iD’s approved list of handsets and I folowed the “3G is being switched off and I can't make calls. What do I need to do?” article and specifically “I’m using a Samsung Galaxy” but I still cannot make ore receive calls. Prior to that I restated the phone and checked for updates. When I dial out it says it is calling but then after a period of time the call just ends. I just took the SIM out and gave it a clean but that hasn’t helped. If I perform a Network Reset it then displays “4G” on the phone which it didn’t before but I still cannot make or receive calls.