Harassment from Builders

Hi, I have purchased the ongoing apartment project in Bangalore 2013. As per the sale deed the project would have completed by 2015. But unfortunately till today apartment is lacking with basic facilities. Project was completed but still missing all the promised amenities and facilities. Also the quality of the apartments are poorly built. Till date OC was not provided. Currently there are 60+ apartments are occupied and no association was formed. Builders are not at all responding for any concerns. We all thought of going legal long back but then Builder has harassed saying if we go legal we wont get our OC certificate. They are not ready to form the association because they dont have the needed documents and also they dont have the required corpus fund to transfer to us. Now they are asked us to pay the high maintenance amount but they are not paying their shares. We are all suffering from this. I have put my hard earned money on this and lost my mental peace with this day to chaos. Also when I ask the builder, I also got the threatening for the same. Please advise me and help me to find the solution for this. Thanks in advance.