Claiming the security deposit back from the landlord

The landlord is not returning the security deposit.

I have vacated the apartment that I rent and satisfied all conditions as per the Tenancy Contract (painted the apartment, fixed and cleaned all -- this had been acknowledged in written by landlord's deputy, cancelled all utility services and Ejari and delivered the landlord cancellation forms).

Upon returning the keys, the landlord's deputy said he would call me when the security deposit cheque is ready. He never called, my email requests are not answered, my calls are ignored since then. Now already 2 weeks.

I do have proof of handing over the security deposit cheque (by the real estate agency that arranged the apartment rental), that it was cached by the landlord and a written acknowledgement that the apartment was handed over with no issues.

What is the correct and most effort-time efficient way to make the landlord fulfill his obligations and return the security deposit to me?

Thank you,

V.