Beeta Agency, Uluberia, Howrah, Wb. — To get full return with interest on cancellation of illegal Flat

Address: Howrah, West Bengal

Almost 10 months back I booked a flat against a token deposit of money without checking papers. Now after checking papers it is proved that the flat has been developed on a "Govt. Khas" area though the current owner of the land managed to mutate(parcha) the land in her name few decades back. Now the Govt. officials has confirmed me that it is still a Govt. Khas area and no further mutation is possible. Please suggest me how can I proceed to get full return with interest. Thank you.