He has committed a fraud on you as encumbrance certificate must have been obtained by you. He sold you a property that had loan on it and took the money and the loan amount too. File a fir against these persons and also a cancellation of sale deed in the district court.

The property now registered on your name is not legally valid because it has been done on the basis of the fake and fabricated documents fraudulently by the seller with the help of agent.

The title is defective 

No buyer will buy the property without the original registered document in your possession.

You may have to pay the entire loan and get a no due certificate besides the bank has to revoke the mortgage loan details registered with the registration department.

Even then the bank will release the property documents to the original owner and not to you.

Alternately you can lodge a criminal complaint against the agent and the vendor for this fraudulent act. 

Seller has to approach bank to handover original documents 

bank will not hand them over to you 

engage a detective agency to trace the seller 

Dear Sir, 

You are suggested to approach the concerned bank and put your points to the concerned staff and deal directly. Also serve a legal notice to the agent for doing needful in specified time limit. 

- Since, the title deed of that property has been mortgaged with the bank , then without getting the same after payment of remaining loan amount , that flat will be considered as banks property . 

- You should lodge a compliant against that agent and last owner for cheating and breach of trust before the police in Ghaziabad and higher official . 

- If, no response and no FIR lodged against him , then file a compliant before the court. 

- Further , without getting that mortgaged registry , you cannot sell legally.