Validity of Allotment for Stilt Parking Issued by Builder

I have purchased Stilt Parking with Allotment Letter from Builder and no separate agreement for it. Respective Flat no has also painted by builder in said parking unit. Also, process of getting Property Tax of said parking unit in the name of Flat owner is under process. Now Society is claiming ownership of Parking Space, reasoning illegality of such transaction and no validity of Allotment Letter under By-Laws of the society, with no rights to builder to sell such spaces. They are planning to do re-allotment with first come first serve basis. My questions as below: - 1. Can Builder Sell such Stilt Parking Spaces based on Allotment Letter? 2. Is there any validity of Allotment Letter in court of Law? 3. Can Society challenge to such allotment, if it’s illegal? 4. If Property Tax Bills get issued in the name of Parking Owner, can still Society claim ownership? 5. Is it possible to get separate registered agreement with builder now (post society handover), if he agrees?