They just said "you're guilty, we'll take your money". It's unbelievable.
I'm sure a casino with a good reputation won't do that without proof. this could be related to the address you used for deposits and withdrawals. maybe you forgot to share the address for deposits with your other account, or your friend's account.
It could also be related to the documents you provide. This also makes sense when you have been banned in the past and created your new account to continue your fun.
the only way you can do this at this time is to contact the representative. but seeing your case, I doubt you will get your money back.