AppleID after changing carriers

We just changed providers, but transferred our old numbers. My son used a QR code to transfer and is using and E-SIM. He is now getting a message that, "The number is registered to your AppleID, but is not associated with the phone. you can keep using the number for IMessages until it expires." Any thoughts about what to do? We tried turning it off and on. Who do you think can help Apple or the carrier?

Thanks