IT WILL NOT DO ANY CALLS INDOORS OR RECEIVE ANY INDOORS,SOMETIMES IT WILL WORK OUTSIDE BUT ALSO VERY OFTEN IT SAYS ITS NOT REGISTERED ON NETWORK,ALL SEEMS ODD,I HAVE TRIED MANY THINGS BUT NOTHING IS HELPING,ALL ADVICE WOULD BE GREATIT WAS PERFECT BEFORE THE SAMSUNG SOFTWARE UPDATE.(CAPS DUE TO VISION)
Check if WiFi Calling has been turned off by the update. Open the phone app, tap the three vertical dots & then settings. WiFi Calling is an option there & should be turned on. You should see this symbol.
Also check the EE coverage here by entering your postcode & clicking Check Status.