when you say "abnormal" what exactly do you mean?
Most likely, they will not disclose the actual reason for what was considered 'abnormal' was that which violated the rules of BK8 through your account and activity.
can any casino steal money like this, just by writing that we consider it "abnormal"?
There is a reason behind that but it's up to them to tell you what is the actual thing you did that made you breach their TOS. But I guess that ends there, you'll only get what they have decided to refund to you based on your accounts LTV.