Landlord not refunding Security Deposit.How to recover it?

I had taken a premises in Delhi Cantonment area (New Delhi region) on rent to operate a coaching centre. I stayed in this property for about 2 years. There is a proper agreement signed with the landlord which was notarised. I vacated the premises on 28th Feb after serving a proper and due notice to the landlord. The landlord is holding 1 month's security deposit and is refusing to pay this money back inspite of repeated communication. The land lord is making one after the other demands all of which are unfair. After fulfilling most of his( and her) demands initially to avoid any unnecessary confrontation, and still not getting the money back, it has become clear that the land lord has no intention to pay back the security deposit. I now need to file a legal case to recover my legitimate money which the landlord is refusing to pay for 7 days now and shows shows no intention to pay . Kindly share the procedure including if it is mandatory to file a police case first.