Registration of flat

I have been occupying a Flat in Noida after purchasing it in the year 2015 and making full payment for it.The Builder has even given possession letter but not allowing registry of Flat.He has Rs 200 Crore outstanding with the authority. Q1)Can I file a case against him in RERA for not registering my Flat and claim damages. 2)He is taking enhanced maintenance charges from the occupants till date.The CC was obtained in the year 2018.Can he collect maintenance legally? 3)What are the damages I can claim for under these circumstances as it is restricting me from becoming legal owner of the property. 4)The Authority and Administration is turning blind eye to these after many complaints.Can occupants form AOA before registration of Flats.