They're asking you to LIST your other accounts in their casino because if you have two or more accounts, then you have broken their rules which you have signed not to break during registration. They are also sort of sure that you have more than one account, which from the chat, you never addressed. You merely posted your other complaints in CasinoGuru.
I saw some user who was asked the same questions, and they kept insisting. It seemed they we so sure about it only to unlock his account after some days. So where is exactly the line between someone who is guilty of having multiple accounts and someone who's innocent.
If you don't have more than one account, then tell them, AND ask them HOW they concluded that you have more than one account, or WHY are they accusing you.
I think he has already told them so, but they keep insisting.
So I guess much better to cooperate with them then try to see if you can help to make the investigation became more faster.
How is he supposed to cooperate assuming he was innocent if they can proceed minus him listing any other account?