Regarding sale deed

Hi , i have sale my flat. Buyer has got loan from L&T finance. We have sale flat in 28 lakh.Buyer has paid one lakh from own contribution and remaining amount pay by bank.I have loan from HDFC ltd with 690000. L&T finance has provide the cheque details for total 27lakh amount. One with name HdFC ltd and another with my name for remaining amount. Now we have done agreement to sale based on the same and mentioned cheque details and amount in agreement to sale.Now L&T finance should release cheque of HDFC ltd for closing the current financial institute loan but L&T refuse to release the cheque and asking for final sale deed. They are saying that they will only give the HDFC ltd cheque after providig the final sale deed. My cheque they will give once provide the original document recived from HDFC ltd. Can you please advice should i go for final sale deed or not in this case? at this moment i have details of the cheque number and amount mentioned on the same. can you please advice me that it will be sufficient for the final sale deed. Also i want to know that if something happen then can i get my property back and able to cancle the final sale deed or not. i have mentioned one clause in sale deed statted that If assignee will be failed to pay all consideration amount within 90 days then this deed of assigment automatically get terminated / cancle and assionor will not be libale for any charges paid by assinee . Regards Ambrish Gupta