They shouldn't take anything since for what I know the exchange representative will not ask any money from their users and impersonators are rampant on social media channels so better verify first this issue to the real one and ask about this issue on their legitimate channels so that you can verify how true the 500 handling fee ask by them.
Also listen to what other suggested to you since they have good pointers to follow and let see if those suggestion could really help you.
Actually it's quite normal for him to have to pay a fee to recover that . He messed up , apparently 10000$ isn't enough for him to make sure that he sent to the correct address.
Theoretically most exchanges wouldn't even give him the chance to recover that , since recovering them would mean access to the private keys , which is a big no-no.
So yeah , having to pay 500 $ to make up for a mistake he made himself , isn't exactly scamming behaviour .