Open and covered parking problem

We have purchased new flat. We booked when construction was going on / building was under construction.(before RERA) Our agreement to sale date is Thursday, 16th march 2017. We are facing problem with open car parking. Builder told us that you will get your parking ownership. Open car parking details are mentioned in agreement as below. In INDEX 2 it has mentioned as open car parking with area 9.29 square meter. In Page no. 26 – Schedule 2. In page No 27 – Specification and Amenities. Possession date is 9th sept 2018.(before Rera was started and site was registered in RERA) MSEB electric connection got in Nov 2018. Letterbox and Name plate received and fitting done in June 2019. We so many time asked them orally to builder/Builder representative about our ownership of open car parking. They not replied to us. At the time of agreement i was ready to pay parking charges. I was in first 15 purchasers members. After that when we had been checked, that in master plan of construction seen that there is no space available for open car parking. There sufficient space in comman parking by can allot parking to all remaining flat owners. Total 60 flat are our building. We are 26 member facing same problem. Other member of society are opposing for allotment of open car parking. We think that in this case we have been deceived. In which case we have possible to re-allot all covered and open car parking? how to get our car parking rights? Which way that would be appropriate for the justice this issue?