What exactly do you mean by "not registered"?
Is that the message that appears on the phone?
Do you have a connection to the 48 network - i.e. signal bars?
If not then if you do a manual search for networks can you see and connect to 48?
If not then what happens - any error messages?
When was everything working ok last?
What changed in the meantime?
Why phone software update or settings changes?
What make and model of phone is it?
Can you try your SIM in another unlocked phone to see if it works there?
Maybe try taking the SIM out, gently cleaning the SIM contacts, reinstalling it, and rebooting the phone to see if that makes any difference?
You might need to try a replacement SIM.
If you need to contact 48 support about this then see the links in my signature below.
