Mutation of sale deed without partition deed.

Hello, I have bought a plot in Kolkata which is a part of the full plot gifted to 2 brothers and 1 sister by Kolkata Municipal Corporation under the refugee act. The 3 owners verbally divided the plot in 3 more or less equal parts and have constructed their own houses. Now I bought one part of the plot from the son of one of the brothers who is the present owner of his father's part as the sole heir. During the sale deed which was done in my name, I was given signed NOCs from the rest of the owners/ heirs of the total plot. The said NOCs may not be valid as they are not on stamp paper but plain white sheet. The seller also has not provided me the death certificates of his father, mother or elder brother as documents proving their demise. I know it is all a lost cause, but can someone please tell me if the sale deed part of the plot that I bought could be mutated in my name and if so, how should it be done. Most probably I have been duped, but is there a way to rectify the mistake? Thanks, Kamal