Cancellation by builder after 80% payment

Case of Noida Extension. Builder made us sign consent in February 2013 for additional FAR and extending possession date till December 2015. Later as there were some issues (job change) to avail housing loan, the builder started building pressure for cancellation due to non-payment. Somehow loan got approved but builder provided agreement by extending possession date again till December 2016. As per pmt. plan 80% has been already paid and 15% to be paid on completion of brick work which has been achieved. Now on one hand builder is demanding 15% but on the other has not provided any reason that after completion of brick work, why 20 months time is required for possession. We are paying EMI and rental and payment of another 15% is going to have added burden upon us for the next 20 months therefore we had questioned the builder and asked for 2 options that either to provide handover within a justified timeframe of 6-8 months and we are ready to pay the demanded amount or raise the demand at a stage when unit can be handed over in 6-8 months but the builder has not provided any reply but to go by the agreement. After sending a couple of reminders (demand raised in May 2015) we've been sent Cancellation Notice mentioning that our unit has been cancelled and the amount paid by us through bank loan would be returned to the bank after adjusting cancellation charges. Can builder cancel our unit in this scenario especially when 80% payment has already been made?? Aren't we justified with our concerns to manage higher EMI for such a long period if we pay 95% payment?? Is there no obligation on the part of the builder?? Kindly advise.