Allotment letter or Possession letter and Parking space

I had purchased a ready to occupy flat, which was a vendor unit. I got into assignment agreement with the vendor and agreement was transferred to me. There was already sale agreement done between vendor and builder and later vendor assignment the agreement to me and finally we did sale deed, registration, paid stamp duty, and now the property is in my name. Full payment is done to the vendor. As per the sale deed I am entitled to get a parking space and benefit of other amenities. Now when I asking the builder to provide me allotment letter and parking space they are denying saying to bring the vendor because they need to collect some dues from him. The vendor is not reachable as I understood he is in hospital. If I don’t get allotment or the possession letter from the developer, will there be any problem to my ownership. Will sale deed, EC and Deed of declaration serve as legal document of my ownership. If the vendor is not able to appear what should I do. The builder has received OC and my flat is ready to move. What should be done to get allotment letter and parking space.