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.
This indeed is very odd, and I haven't hear of any exchange to do just that. Perhaps your transactions somehow flagged up as suspicious and they're investigating this, thought whichever the matter I feel they should communicate it clearly. It's such a nuisance but I suppose the best course of action is to get in touch with them to find out why this occurred and how can you/they remedy this so that both of you walk away happy.