Fine for a cheque returned as unpaid

Hi, I have a problem. The house owner in UAE, Dubai asked me today to pay a fine for returned cheque 5,000 AED in case the cheque bounced and it is written in the contract.

Today they called me asking for the fine anyway they say they gave the cheque to another bank to collect the money and the other bank rejected it. I called my bank and they said no one gave them any cheque. So the owner wants the fine and the rent. What should I do?