About extend the sale deed and suit law against seller

I have registered the sale deed on june 15th 2015 for the sum of rupees 5Lakhs. The balance amount to be paid is 7.5Lakhs. As per the sale agreement , our agreement period is 2 months from the date of sale deed agreement. I have paid this amount to the seller only on the ground of court order.( the seller has not original 'thai pathiram' of the property) After, I approached the bank for loan amount that they said that this is the invalid document due to the absence of legal heir certificate . so i am not able to get the loan and also I have sent the notice to seller by our lawyer. But the seller is not ready to give the document. In this situation I am not able to do anything. Can I suit any case against the seller( for not giving the legal heir docs) or extend the sale agreement period legally. Note: I orally talked with seller regarding the extension of the sale deed time period hence he is not ready to accept this. we have been in the house for more than 70 years. We paid the eb bill, property tax etc in the name of my grandmother upto 2015 dec. After (June - 2015) getting the court order he changed the patta ,water bill , property tax and eb to his name. I am not interested at leaving this house Kindly advice.