what prevented you from taking advise before entering into the transaction?? now after having comitted a mistake yoru are seeking advice that too without naration of adequate facts.
A sale does not take place without possession is the law. you have not disclosed as what is written about the possession in the sale deed. was it disclosed to you that property was mortgaged with bank. did you made due enquiary about the title of your vendor owner that property you were to buy was free of all encumberences. If yor vendor concealed the fact from you that his property was mortgaged then he has comitted FRAUD against you for he is liable criminally as well as contractually and you are at option of exercingboth or any of them but you can secure your consideration passed to him ony by filing of civil suit within jurisdiction the property situate,or your vendor reside praying court to declare the sale void on ground of fraud played upon you by the vendor and return of consideration and siam duty and all expences incurred by togather with damages caused to you;
The next alternate is to compel your vendor to discharge the debt as soon as possible and take over possession as soon as possible.
And if you jump into the transaction seeking some bargain then you can choose to deposit the dues of the bank on your own and get the mortgatgage redeemeed andretired from your source of money and then file the suit of recovery againt your vendor for money paid to bank .
Mind your vendors' property was encumbered with debt of bank and in law you have purchase both the property as well as debt,so if you to retain the property,the only course open to you is to deposit the debt and take a discharge /reedemption from bank and its NOC too.
So again it is your option to choose among different courses advised by me to you.
ONE MORE CAUTION IF YOU CHOOSE TO AVIOD THE SALE ON THE GROUND OF FRAUD AND WANT YOUR MONEY BACK YOU WILL HAVE TO FILE THE SUIT WITH IN THREE YEARS FROM THE DATE OF KNOWLEDGE OF FRAUD>BETTER EVEN IF YOU FILE SUIT WITH IN THREE YEARS FROM DATE SALE DEED SO THAT NO QUESTION LIMATATION AND TIME BARING DEFENCE ARISES FOR CONTEST IN YOUR MATTER,
hope it goes well with you.