No Possession Certificate. Can I hold back Corpus Fund?

In 2013 we booked a Flat in Pune. The builder promised to give flat possession by Sept '14. The project got delayed by 9 months and since there wasn't any clarity on possession dates , we shifted in our flat in June'15, following the footsteps of 25 families who shifted without Possession letter from builder. All families living in the society are yet to pay Maintenance and corpus Fund money to the builder. Time and again we have requested the builder to provide Commencement certificate, Occupancy Certificate, but despite of repeated request, builder is not providing us any document/ certificate. Now the builder is asking that we directly apply for Possession certificate. In addition to this the builder is repeatedly demanding all of us , the remaining Maintenance and corpus fund amount. Few amenities are yet to be ready by the builder, in addition to this there is no clarity when the remaining phase of the project will get started. We are little skeptical on this, as this looks indefinite delay. Please advice what shall we do? Shall we clear all dues before getting Possession/ occupancy and completion certificate. Am I legally bound to pay Corpus and Maintenance money to the builder, despite builder not providing any Govt Certificate, or completing the amenities?