1. You have been grosslyb cheated by the seller.
2. It apperas that the said flat is under mortgage with the lending bank and as per law, a mortgaged property can not be dealt with in any way including selling.
3. The sale deed registeered by you by p[aying stamp duty is invalid for reasons stated above and itt will continue to stay as invalid even if the seller rep[ays the loan.
4. The procedure to buty such mortgaged property is to enter in to tripartite agreement with the bank, seller and yourself wherein the bank will agree f0or the selers regist6ering the sale deed in your favour and yopu shall pay the consideration to the seller by depositing (handeing over to the bank representative present at the time ofregistration of the sale deed) the cheque to his loan account.
5. When you have already paid the consideration, the seller shuld have paid the balance amopunt to the bank and is avoiding to make such payment.
6. The seller might avoid payment fo the outstanding amount and in that case the Bank will take possession of the said flat by initiating SARFAESI proceeding and sell it of to recover its outstaning dues lying in the loan account of the seller.
7. Lodge a policfe complaintant against the seller for chjeating you and thereafter file a Recovery Suit praying for an order directing the seller to return yuou the amount paid by you with interest, danage and cost.