iMessage doesn't work after ported phone number (change of carrier)

Hello! I have ported my number (changed the carrier) and during the process I received a new SIM with a temporary number. Now that the process was completed (2 weeks ago), calls and sms work properly, but I cannot get iMessage and Facetime to work with my number, because the iPhone is using the temporary phone number.

In Settings > Phone > My Number is set the temporary number, and I cannot change it to my old number.

How can I solve this and use again iMessage?