What they are doing is literally robbery and they should be dragged to court.
Good luck with that... especially when your lawyer will ask you about the ToS.
This doesn't mean that it's okay that they don't refund the money, I lost about 1 BTC myself from my account so obviously I'm not happy with it. But the most efficient way not to get ****ed again is just to set the auto payout threshold as low as reasonable (i.e. at least once every day).