Tata Docomo, to return the Security Deposit

I made a security deposit of Rs. 899/- to Tata Docomo at the time of taking the connection. However I have now disconnected my connection with Tata Docomo for the enormous number of problems they gave me when I was with them & moved back to Vodafone which was my previous service provider. Tata Docomo still hasnt returned my security deposit (Rs.899/-) even till date, even after 3 or more months…Also, I disputed my last bill & one of the operators (A girl operator – cant recall her name) who spoke to me about that bill, had agreed to waive away the bill and had confirmed to me suggesting that I would be given my whole security deposit as it was an error from Tata Docomo’s end. Nothing received till date & also I had visited the Tata Docomo store recently only to know that they have subtracted the last bills amount without even my knowledge & havent got back to me. A supervisor by name Nagaraj, I last spoke to (2 weeks back approx) said, that he will listen to the previous call where the girl had suggested & confirmed on being Tata Docomo’s error & that he would call me in 48 hours time to let me know on the status… wonder! how they calculate the time because till date I have heard nothing from them. I need my money, they cant take their customers money for nothing. Hope to get some update from them after this.