Do you have further evidence to prove that everything you say is true and that you actually made a deposit into Stake casino, i don't think this mail is enough, but i'll wait to hear what other users think. That being said, in the meantime if we agree that you are telling the whole truth and the casino believes something was wrong with your KYC, aren't they supposed to confiscate your winnings only, allow you withdraw your deposit and close your account.
https://imgur.com/a/5DqjiGzThat screenshot shows my deposit and current balance on the site that's been stolen from me. Please also note that my KYC level 2 was approved before I made a deposit. This was to be safe and to ensure something like this would not happen, but instead they retracted the KYC only after my deposit and locked everything in there.