Completion Certificate

I have purchased a flat in a big housing project in Kolkata. The total project is not yet completed with all amenities promised. Phase by Phase block is completed. My Block is completed in Feb 2020 , but Completion Certificate is yet to obtain from builder. As per the agreement, it was written that min 6 months time is needed for Completion Certificate ( CC), but time has already exceeded to almost 1 year. After asking builder, builder says that it is under progress and a maintenance charge is also demanded from the builder month wise from June 2020 to till date. As , I had not taken any possession of my flat rather I demanded CC from the builder , telling maintenance is not liable under CC is given to me. But, the builder is pressurizing me to pay the maintenance charges, as other people are paying maintenance and they had taken possession without CC. On the other hand my flat construction has been delayed for atleast 2 years ( as per agreement it was written maximum 3 years & 6 months) and till now no association of the buyer has formed So, my question in this case is what to do, is it legal to take possession without CC & paying the maintenance charge without handover.