What is written on the TOS is irrelevant: they cant keep your money without presenting a very good reason. Suspending and terminating an account is one thing. Keeping the balance is another. You wrote you deposited years ago. You are talking about real bitcoins or just fractions of 1 bitcoin? If you have there some bitcoins you will have reason and ground to move this to a finish court. But you can try first finish financial regulators.
https://www.finanssivalvonta.fi/en As another member posted you also should post evidence hiding any sensitive information.
They can suspend or terminate the accounts which doesn't accept their terms after the time period given for them to decide, as most common I am not storing more than a bitcoin in any of the exchange no matter what and OP may also fall onto category from my assumption. Even if the amount worth millions now still its hard to retrieve but he can know the reasons via support ticket, the same kind of scenarios happen even when the user violates their terms and another user reported to support with proper evidence.