Certified copy not accepted by the bank

I am buying a resale property which was on mortgage with United Bank of India against a house building loan. However i did a down payment by which the seller was able to clear the loan and get a NOC from the bank. then i applied for a home loan in a nationalized bank, after my profile verification i got a sanction letter of 20lacs, but later on the bank said the property is in panchayat area and is not of that value and they gave me a revised sanction letter of 15 lacs, in these processes it’s almost 2 months now. 2 days back i received a sms that my loan has been disbursed, but now they are saying that the original mother deed of the property is required which unfortunately the seller doesn't have, i asked them if i can produce a certified copy of the same but they are saying that because the property is in panchayat area it will not be considered. Now it was in 1994 when my seller bought that land from someone and they have no clue where the previous seller is now. . The bank is now asking me to write an email to them asking to cancel the loan. What should i do. Please advice,