Non completion of redevelopment project

My building went for redevelopment in feb 2015 and the project had still not been completed. All flat owners have individual contracts with the builder according to which the completion and handover of the flats (with full NOC) was to be done in 2 years + 6 months grace period, failure to which the builder was to give us a penalty amount over the agreed monthly rent. The first 3 years we were paid regularly after which he started faltering. However, since the last 1 year the builder has not been giving us the agreed monthly rent amount forget any mention of penalty and we’ve been paying out of our pockets. Also the work on our project has come to a complete standstill. I would like to know what are my options here to deal with this situation in the most economical and timely way possible. Also I believe we cannot go through RERA as the project completion date is registered as Dec 2020