But they are all centralized exchanges, they can seize your coins. But if you have nothing to hide that is a crime, threaten the exchange with lawsuit would be best.
Threat won't be enough, I think that OP should just straight up file the lawsuit, pretty sure that a threat is easily brushed off and I don't think that you're going to have a hard time doing a back and forth inquiry with threats of lawsuit so you're better off doing the lawsuit because a subpoena will definitely make them lose their minds and if they don't answer to it then the exchange will lose more than just the 100k that they've stolen from OP, and the actual lawsuit happening instead of threatening increases your chances that you will get more money and if they fight it even if the exchange itself know that they're in the wrong then they're going to pay more to OP besides the legal fees. So don't threaten them with a lawsuit, file it already.