Cannot verify child's account
I am in a constant circle of trying to verify my son's Apple account due to an old phone number being linked to it.
I cannot find a way to verify, or even start a recovery process as it wants to send a text to his old, inaccessible number. And when an email verification is selected, no email arrives. I have tried receiving text instructions to my own phone, but then it just says 'too many codes sent.'
Any help appreciated
iPhone XR