iPhone settings have not changed after porting

1. My iPhone thinks my number is the Lebara SIM number, despite porting back to my previous number
2. I have a message telling me my old number is registered to my Apple account but is not associated with this phone.. 28 days left.
I assume they are related.
Tech support were slow and unhelpful.
Is there a reliable fix?

AndrewF5 just to clarify you've joined Lebara and your phone is still showing the original Lebara number and not the number you've ported in?