Harassed by Employer-Need Help (Dubai)

I worked for a company in freezone as a Key account manager for Executive search. I had a limited term contract for 3 years with a probation period of 6 months. I did not like the environment of the organisation and I resigned in my fifth month. The day I resigned, my employer asked for my passport and said he will initiate the visa cancellation process. He also mailed me that I will have to give the hand over. I continued working for 4 more days and gave all the hand over. Post that my employer mailed me that he would cancel the visa if I pay him 45 days salary to which I was shocked and I told him that I will not be able to do so. He made me sign a resignation which state that I can pay him within three months and he can put a ban on me.

Post that he went to the free zone authority and complaint against me for breach of contract.

My contract doesnt say anything about paying my employer if I leave in the probation period.

He is constantly harassing me by asking me to pay him 45 days salary and he has kept my passport with him.

What can I do in this case. I require assistance.

Regards
Puneet