Seller had sold a disputed land. Need legal remedy

Had purchased a plot during March’ 2018. Further, I had taken a loan of around 60% of plot value from Bank. During January’ 20 when we were about to construct the building on our plot, the other buyer of plot appeared and claimed that the plot belongs to him. Finally, after prolonged discussion and verification, it was found that other buyer is legal owner of property. Seller of my property has admitted that he has made mistake and agree to refund our amount verbally. We continue to follow up for the amount, however, still we have not received the amount. While we are inclined to settle this mutually, however, need a legal remedy on following issues 1) Whether I can file the fraud case against him? If yes, what is period generally local police take to initiate the action against the accused 2) Is there any legal action I can take against bank as the bank had also done legal verification of title before disbursement of loan? Just want to highlight that all the payment (apart from bank loan) made to seller from my account to Seller account