BUILDER FAILED TO HANDOVER THE POSSESSION

Dear Sir , we were alloted flat by builder in NCR region in the year 2007 which was to be completed in 3yrs time i.e. 2010 . Flat cost was 34.17 lacs & by june 2008 , more than 60% payment was already made . Over frivolous reasons threat of cancellation of the flat was being made despite the fact that progress was far less than the amount already paid. Further , meeting was held in June 2015 to stress that threats of cancellation are baseless and to either refund the amount paid by us or to give the possession of the flat . We were assured that if Rs. 10 lacs more is paid by us , the possession will be given in a yrs time . We thus immediatedly made the payment of Rs. 10 lacs which is about 95% of the cost of the flat. It is signifiacnt that as per agreement , builder stated to claim 18% interest for delay in payment by us. On reciprocal basis present day cost of our claim ( amount paid + 18% interest ) comes to more than 1.5 Cr. Kindly suggest legal remedy .