What happens when you try to make a call?
If outgoing calls fail with both a Tesco and a 48 SIM then that suggests an issue with the handset.
Have you tried a factory reset?
What make and model of phone is it?
Were you ever able to make calls?
If you want a new number (and you'll lose your old one) then contact 48 support and see if they can assist.
See the link in my signature below or email them at email@example.com