1) you have to inform HDFC that you have cancelled the agreement
2) out of refund received from builder you have to repay loan taken from HDFC
3) it is not in your interest to cancel the agreement now .
4) most of builders are facing financial constraints and there is delay in refund
5) in many cases flat purchaser has to go to court and obtain orders to direct builder to refund money
6) further you are losing 10 per cent of payment as cancellation charges
7) take possession of flat then sell the flat