i've no intend to return back:) i'll fight for every sat:)
In that case, you won't get a nut. It's not an ethical move from the exchange (I never heard before this time), but if you don't cooperate them, you are losing both BSV and your BTC. So, I think you must follow the step they ask and get your BTC back. That will be a win for you.
Maybe they are not returning that to that dumper at all? They could give BTC rate at which OP bought BSV and get those BSV and turn that into their profit. You can't trust such unethical exchange. They have no right to interfere like that. If it were an technical error then could have been understandable but that's not the case.