I had booked a flat (under construction) with a reputed builder. As per the agreement signed, they were supposed to do the allotment within 9 months, failing which they were supposed to pay 11% simple interest. After 15 months also, when the allotment was not done, I filed for a cancellation. After much arguements and discussions, i finally got my booking amount back but not the interest amount. Kindly advice on how to proceed further.