Why is my temporary number still showing in Message?

I can remove a temporary number from my phone, and cannot get my actual number on iMessage.

I've changed provider, got a new sim and a temporary number. I successfully changed to my number, Apple account knows my number but Sign in & security says my number not available for iMessage and Facetime. The temporary number has been been removed on my Apply account.

BUT... The number showing in Phone app, iMessage and Facetime is still the temporary number and I cannot remove it.

Message is 'You must have a SIM associated with an Apple device for +44 7*...'

I feel like I've tried everything. Signing out, switching off, removing sim, in all combinations. Nothing works.