iMessage and Facetime Issue

I recently changed my server and my mobile. I switched from Virgin to Giffgaff. I took my old number with me. However, until my old number had been transferred I was given a temporary number. I received a message asking if I wanted to connect iMessage and Facetime to the temporary number. I decided not to do this. Despite this, I have found that it has been attached to iMessage and Facetime. How do I remove this attachment of the temporary number and replace it with the phone number I've transferred over from Virgin? This number being the one connected with my Apple Id. My new phone is the iPhone 13 Pro. I am able to receive and send messages using the number transferred over from Virgin, but would prefer to remove the temporary number from the phone, as I don't need it.