cheque given by builders not encashed,fear if i willget the flat inste

fathers plot of 99 years lease with old construction on it given for redevelopment to a builder 4 yrs ago.registration documented for getting 3 flats as compensation .my mothr and myself ask for money instead of flats to the builder. next day he gives both cheques as decided and he makes us sign a receipt with no letterhead stating that we both have received cheques with so and so date and numbers,amount as full and final paymentof consideration in lieu of surrendering 2 flats of 500sqt to be alloted under the terms of the Development aggrement dated 8-8-2014.(previos day).the receipt was dated 9-8-2014.Next he continuosly delayed us and request that we should not encash the cheques as he had noy put money in the account .the cheques expired.he gave us new 2 cheques dated 2-1-2015.again chequs expired as before. On meeting builder advises us to take flats.Inspite of signing the receipts will i get flats?IS MY REGISTRATION OF FLATS DEED STILL VALID IN COURT?What should be done .