parent rights and international move

I have escalated this 2x now... I set up my child's account and we no longer have access to the uK phone number, can't get into email b/c we need the code sent to the UK number....it has been a nightmare trying to get my son's account recovered. he can't even use the phone b/c it is locked to his apple id, which we can't get to! I have his password, just not the UK number and I have been told it can't be sent to my number either. so frustrating that it is a child account, yet, I the Parent assigned to it can not access it, what is the point of a child account if the parent can't access it???