Auctioned property.

One property is mortgaged in the bank.  This property is not auctioned but the owner has made an agreement for selling the same at sum of Rs.3,00,000/- .  Now there is boom in the prices of land in Guntur the owner is not willing to sell.  When I approached the bank, the bank authorities had said that they are no way concerned with the amount the owner has taken.  Hence at this juncture how should I proceed legally to achieve the property.