Consumer Redressal

We have booked a 3-bhk flat in Cosmocity-3 project of the builder M/s ERA Landmarks Ltd. in Sector-103,gurgaon.The builder on already taking 32.5% of the BSP of the Unit(62.5 lakhs)made us sign a BBA on 06/07/13.Thereafter raised the demand for 12.9lakhs as the BBA which could not be paid before the due date (24/08/13 later revised to24/09/13)as the bank loan could not materialize in time.When we approached the builder on approval of our bank loan on 05/12/13,he says the unit is cancelled and allotted to someone.He insists a letter from us for refund so that he shall refund after deducting 15% of the BSP of the unit(not the booking amount) and other commission charges etc. as per the BBA which finally will fetch me only peanuts.Please help me come out of this by getting back my full amount.