Possession of Flat & Registration without completion certificate from the municipality

I have purchased a residential flat in kolkata in a multi-storied building having total 20 flats. I have made full payment to the builder. In March 2018 the builder gave me the possession of my flat after doing registry of my flat, without obtaining completion certificate (CC) and occupancy certificate (OC) from the municipality. About 16 Flat Owners have made registration of their flats and taken possession without CC and OC. My Queries: 1) Whether it is legal in Kolkata / West Bengal the registration of sale deed without CC and OC ? 2) What can be the dangers if a flat owner has done the registration and taken over the possession of flat without CC and OC ? 3) At the time of registration of my flat, the builder had collected Rs. 25,000 for "One year Maintenance Security Deposit'. But now the builder is saying that maintenance deposit will be kept as Security only (for emergency purposes), and asking me to pay maintenance charges from April 2018 to March 2019 @ Rs 2 per sqft, irrespective of whether I have occupied my flat or not. Is it legal ? 4) At the time of registration of my flat, the builder did not incorporate the clause in Sale Deed that the builder shall give CC and OC within a specified period of time (inspite of my request in writing to the builder) ? 5) Builder is saying that the Flat Owners Association cannot be formed till CC and OC are given. Is this true ? 5) Govt. in West Bengal did not implement RERA and instead implemented their own real estate regulatory authority HIRA (WEST BENGAL HOUSING INDUSTRY REGULATORY AUTHORITY). 6) Is there any remedy for Flat Purchasers in HIRA regarding not providing the CC and OC within a specified period of time ? 7) I had purchased my flat under a home loan. I want to occupy my flat as early as possible as I am not able to take income tax benefit of interest and also paying rent and Loan EMIs. 8) Please advise me what should I do ? Best Regards, Rajesh Kumar Mobile: [deleted]