Cancellation of flat after agreement of sales

Hi i have booked a flat in pune _under construction.. i have also took a loan against that flat from HDFC... 70 % of the loan is disbursed... i want to cancel that flat. I dont have the money paid by bank to builder... HDFC says pay the money and close the loan ....builder is saying give the original agreement and we will give you back the money received by bank... i m confused please help... also what abt the stamp duty and registration charge paid to gov... Thanks a lot in advance !!!