Related to delayed completion of buidling

HI, I have a flat which was booked in April 2015. Which possession was expected in Dec 2015 , But we got in Sept 2016. At the time of possession many things were incomplete like lift, compound, podium, top 2 floors and all. Now builder is giving reason that due to road permission passing nearby building is pending he will not be able to complete rest of the things. Due to this no society formation and hence we are facing many issues. Every time builder ask us to pay money for lift maintenance and all. Can we sale our flat in this condition? Is there any issue in this? Or can we have some legal action against builder? He is from political background so can we have some action which will be safe for us? Can we have some help from RERA ? Please reply as soon as possible.