Update: Update is that there is no update, because they just don't respond anything. This case is marked as unresolved on AskGamblers as well already.
You know why that they don't respond? Because there was no actual reason to close my account other than that they don't want to pay out winnings.

Anyone can start a online casino, accept all players that lose (and maybe pay out small wins, since like 99% of gamblers lose anyway) and when someone wins a decent amount then just close your account for whatever reason (that doesn't actually exist) and refer to their ToS. That's the area of online sportsbooks right now.