It turned out that they had such a point of the rules
The Customer guarantees not to disclose any information, obtained from the Service support operator, in any channels of communication. Violation of this rule will lead to the account termination without refunding of the remaining balance of the account.
but before that there was no such point!
Whether that clause was there recently or from before is irrelevant, it is illegal for them to refuse to return your funds to you. That's theft.
The most they can do for your supposed contravention of their T&C's is to bar you from using their services. They are not, under any circumstances, entitled to claim ownership of your balance on their platform as a result.