Tbh I don't even know what btcpop is until I read this topic. What makes this unpopular exchange so special for you that makes you want to deposit your fund there?
My guess is that OP bought/sold some shitcoins there that were only available at that exchange and nowhere else, as that's the most common reason why people end up using those dodgy less known exchanges.
@OP Yeah explanation that they have you is a pure bs, and they obviously don't intend to give you back your ETH so they came up with something ridiculous, hoping that you will give up. Good luck with your lawsuit!