RouxB, that's awful.
You might try this: go into your account, and click "request money" and enter the bastahd's email/account, enter the amount and add a note saying it was mistakenly paid, and request an immediate refund.
If you get no response, try clicking the "resolution center".
If you used a credit card, contact the credit card directly. If you used your bank account, contact the bank.
Good luck.
