What procedure needs to be taken when builder has cheated?

I'm speaking from Sakinaka, Mumbai. I wish to seek your help. I had purchased a flat which is under construction and is being restricted to build for some time because of CC issues. Total consideration was 1crore + of 2BHK flat and I already paid 60 lakhs plus the registration and stamp duty fee Rs. 3 lakhs. Also, we have all the legal documents and net transfer details that we have paid the amount to the company. The flat which we had booked and had received an allotment letter, when we asked them to register it as soon as possible, they are continuously delaying and some days back we came to know from other sources that it has got registered. There were many background issues going on with builder and the seller, investor, buyers, etc. Now it's been one month since they have made us pay stamp duty fee in government account but are not registering our flat. What should we do ? People say the builder has literally got no money so if we ask him to cancel and pay us back, he would make us beg for our money for years. What should we do in this case ? And can we file a complain in RERA? Please suggest me some possible ways or procedure. You can email me on [deleted] or call me on [deleted]