More times same person sale a property with mordge loan.

Dear Sir I have a big problem with my property. My father purchase a property in the year of 2011. That was a joint property. thatswhy my father lodged a case in the year of 2010 against property owner if u want sale the property that i want to purchase it otherwise u cant sale any other persons. Bt that time he was sale the property to 3rd person when the case was running. afetr 1yr the the party was nt take his possesion. then my father was purchase the property from 3rd party who already purchase it through registration deed. And as a confirming party was in deed was main owner of the property. Suddenly in the year of 2015 my father was no more. and already my father was changed the mutation of my father name. But current situation is that the main owner still the possesion in my property as a agreement rest basis. but befoe 1 week i saw that some of bank employee come into the property when i asked them they told me that in the year of 2004 the main owner creat a sale deed the name of Kaushik Sen and its mordge by bank loan. But from 2004 to till date kaushik sen not come into a property. But original mother deed is till now in my hand. thay have a pertion deed. as per that pertion deed the creat a sale deed. So what is the process of that how can i get my property back.