Stalled Construction Project and delay in flat possession

This is regarding my case filing against Builder for their RERA registered Project ,Kharghar , Navi Mumbai. Back ground information is that: (1) I booked & registered sale deed of two 2 BHK flats on 8 th Oct.2014. Date of Possession mentioned in the sales deed is within 5 years from the date of Environment Clearance which is 3rd Sept. 2014. So the possession date is due since Sept 19, but the construction work is stopped from August 2017. I have paid full amount to the builder and stilll waiting for the flats possession. Now I am looking for compenastion from the builder for delay in possession. For kind information,the builder has given project completion date on 31st.Dec 2022 during RERA registration which is not in line the date of completion promised to me in the sales deed. (2) The builder has taken additional 23 lakhs approx. from me in March 2016 ( which is extra from the full money paid for two 2BHK .All payment is cheque payment including additional money) and he promised me to return the money with 21% p.a. interest but he has paid nothing till date.I said he to give me allotment letter of one more 2BHK from the unsold stock in the project so that the additional paid amount will be adjusted in the deal.But nothing happening despite several reminder. Now, I am looking for the allotmen letter & registration of 2BHK at prevailing rate at that time from the Builder and if not,he should return the money with interest. I am looking for legal advise and wayforward to sue the Builder to demand compenasation for delay in possession, allotment & registration of another 2bhk from the Builder. I also want to know about expected timeframe for RERA order and what can I anticipate from the order. I also want to inform that there are several number of buyers like me who are facing similiar issue with the builder.