Developer denies Interest for delay in possession

Dear Sir, I along with my father jointly booked a flat with a reputed builder in a Mall cum Residential complex on August 2010. As per the agreement we were assured to be given delivery possession of the said Flat on or before 36Months from the date of allotment with a grace period of 6 Month. As per the agreement we are entitled to receive interest @ 12% per annum on the amounts paid by us from time to time for any delay in delivery possession. The total amount due and payable as per the payment schedule has been timely paid by us till date. Despite regular follow ups we have not got the possession of the said flat nor are getting any confirm date regarding possession. The Builder has also refused to pay interest as per force majeure clause citing reasons like delay due to municipal clearance, delayed payment by other flat owners, local problems etc. However Flats booked after August 2010 in other blocks have been given possession There is already a delay of around 18 months and by looking by the current status of my block in which the flat has been booked looks like it will take 12 more months before delivery of flat Advice required on the following points 1] How to get the delivery or possession of the said flat. 2] How to get interest for the delay in delivery or possession of the said flat. 3] If I take any leagal action, can the builder deny or further delay the delivery of the said flat