'there was over 2300USD in the account though - why would it be closed now without the option to withdraw this?'
Based on your statement I came to know that the KYC document you have used is delisted/blacklisted by the gambling site for the law of the country of your document. As it is out of their policy I mean policy violation they have the right to close the account without returning any winnings. I think if you were not able to withdraw any funds then they would consider enabling the withdraw of the winning amount.
It is not necessarily that a gambling platform restrict access for user residing in certain country simply due to the law of that country, for instance, prohibit gambling activities and casino business. Even when a country allows gambling activity, when a casino or a provider does not have a permit to operate on that country, they'll still put these countries as prohibited territories. It is for the sake of compliance and licensing.
As for withdrawing the winning amount, though every casinos has their own approach on ToS violation, majority of them will refund only the sum of initial deposit or if the user is at total loss. When a user who violates ToS is in overall profit, the rest of the winning amount will be confiscated to "recover" the casinos' monetary loss from those violation.
This should answer why Rollbit also didn't allow withdrawal of OP's winning amount, as OP already withdrawn more than the sum of his deposit
[...]
'Looks like more than the deposit was already returned'
'there was over 2300USD in the account though - why would it be closed now without the option to withdraw this?'
'Looks like more than the deposit was already returned.'
