Housing Project OC without ammenities

Hi, We have booked under construction flat in project with amenities when it was 90% work done in dec-16, We have done registered agreement by paying due amount for 90% Final delivery date mentioned in agreement is June18. Now after Rera ,builder taken different rera no. for each 2-3 buildings separately in same project making it in phases and proposed date mentioned on last building phase is 2020 on rera site,whereas my building rera completion date is dec 18 on rera website. Now builder asking me to take possession of flat in my building by completing 100 work inside flat,so that he can start charging Maintenance charges. But No amenities are ready yet, he has completed podium civil work. If building is taking advantage of separate Rera no. with last completion on 2020, I dont think he will finish any amenities till 2021. How to deal with the situation. what are losses customer has to bear if he cancell flat as builder not delivered as per promised amenities.Most of customers has taken flat considering open space with amenities,greenary but same thing is missing now.