property fraud

First understand that you are a borrower of the bank and you are bound to return the amount, security is a secondary aspect..  When the purchaser is not having knowledge on such sale transactions, as huge investments of life savings are to be catered to getting a home, professional advice and guidance is a must..  Show documents and get a bit of professional advice, as the details you have provided lacks clarity.

I fully endorse the advice of Sri.GLN Prasad.

Nothing more to add.

Criminal complaint is one solution.

Such transactions are quite common; obviously, you alone may not be the affected party. As such, you should try to take a common stand. In my understanding, being the innocent third party, you are entitled for protection of law.