Ground floor flat shown as Garage in Water department plan

Hi, I m kapil teli, resident of Vile-Parle west, Mumbai since birth. My parents had purchased a 1BHK flat at ground floor from the builder in 1976 in a society. The society has ground +5 floors with a lift since then till today. When the re-development process started in the society, our appointed PMC brought to our notice that the development plan of the society from the water department shows our ground floor property as garage. (Since the BMC plan is not available for our society as file is missing or lost or stolen). My question is: how is it possible that my ground floor property is shown as a garage since we have share certificate, water connection, electricity connetion, all BMC property tax paid bills for the said property in place.since possession till today. What can be done to get the ORIGINAL missing plan of the BMC for our society. How do we revise the plan to include our ground floor flat as a FLAT from existing garage shown in the old plan.? Please advise and help. Best regards, Kapil teli