If they wrote that the KYC was completed, then it is impossible that you have more accounts.
I would also like to know from Sportsbet based on which terms did user was accused for multi accounting.
And why was the user able to create more accounts, and sportsbet only jump to the conclusion on the moment he has 8800$ in his account.
If he really owns 4 accounts, why did you guys not inform him when he made his second account? Your software should be able to detect that easily.
OP should be paid in full in this situation. If they refuse to pay you, I suggest to contact the master license holder and the gambling commission if they confiscate the funds.