Help Not registered on any network


Hi all,

I'm getting the old 'not registered on any network' fault. I've tried to have a read up but have had no luck.
It's for a Samsung Galaxy S2 running 4.1.2
I have tried:
1. Soft Reset (off and on)
2. Hard Reset (factory restore)
3. trying to select network (however tesco mobil isn't a choice, but choosing automatically says I have registered on network, but then won't allow me to call)
I cannot phone or text however I can use mobile data (mobile data box is checked and I can connect to internet)
All help appreciated