If I were you I would offer to settle. Point out that you'll fight the case on the basis that, whatever the receipt says, the 'deposit' was in fact an admin fee and charged for services provided to the tenant rather than held as security for his obligations. When working out an amount to offer as a settlement consider that if you lose you will have to pay back the amount of the 'deposit' plus a penalty of at least the deposit amount again and possibly up to three times the deposit at the discretion of the judge. You may also have to pay the tenant's court costs.
The above represents my own opinion, derived from personal knowledge and should not be relied upon as definitive or accurate advice. It is offered free of charge and may contain errors or omissions or be an inaccurate opinion of the law. I accept no liability for any loss or damage suffered as a result of relying on the above.