How to recover money lent to a colleague with just voice messages as proof?

I lent AED 4000 to a colleague of mine. He didn't return them. I also have information that he borrowed from other people but didn't return as well.

As proof, I have voice messages of him saying how much money he owes me and I have his passport and Emirates ID.

What is the procedure I should take and how much money will it cost?

Thank you very much.