Did you tried asking them about it via support? Maybe they can give a better reason about your account being frozen but totally erasing your deposit is really untrustworthy behaviour.
Upon searching there aren't any scam accusations yet but there are quite few reports about manipulation with trading volumes but I guess its common with most of the exchanges but yet there isn't much of a solid proof.
I know Bitforex is doing washtrading and have fake volume, but I am not sure about scam thing.
Maybe they don't allow multiple accounts.
Did you contacted Bitforex support?
In that case they can return back him the amount and delete his account and block him from accessing the site. I don't think they are entitled to punish him by taking all his balance.