My name isXXXXX and I'm happy to help with your question today. I need to ask you some preliminary questions to be able to help you.
14-days is correct. But the time limit starts when the police get the drivers details from DVLA. But the botXXXXX XXXXXne is that your son has accepted the penalty and there is no appeal mechanism to investigate whether he did the right thing or not. Once the penalty is accepted that's the end of the matter.
he has received his fixed penalty but not paid or accepted it yet.