purchase house in bank auction , unable to registry

Dear Sir, I purchased a house from bank on baroda in auction. I have sale deed and old registry that defaulter mortgage in bank with me . Now after 3 to 4 year later another bank (Citi Bank) send notice at my house saying this this property is attached with them on behalf of home loan. Defaulter look fraud home loan on this property from citi bank. How my case is pending is court and citi bank is not able to produce original registry in front of court. please advice me how can I overcome from this prob.