Delayed possession

I booked a 2 BHK 990 sqft flat with a builder in Noida Extension (West) in 2011. The BBA was executed in March 2011 with possession in 30 + /- 6M from signing of agreement / excavation date. I have paid 10% on booking; 30% in 45 days from booking; thereafter 10% each on 1st , 4th, 8th, 12th, & top floor casting. i.e. upto 90% payment has been made as on October 2014. I am 64 years now. I have paid all demand of the builder from my old age savings. The structure of the tower was made ready in November 2014 and thereafter the builder has not undertaken any work in respect of finishing work. In some of the structure of other block’s towers are still unfinished. As per the BBA, executed in March 2011, the possession was due in March 2014. Thereafter the builder informed in 2012 in writing that possession has been revised to June 2015 +/- 6 M. In early 2015, in a meeting with buyers, the builder informed the possession in March 2016. Again in a meeting in Dec. 2015, the builder has informed another date of possession i.e. Oct. 2016. But the ground picture shows that the builder can only give the possession in end 2017 and that too if he starts the work now. In the BBA, the builder has mentioned penalty clause for the buyer that if any instalment or payment is delayed, the would charge 18% to 24% whereas for possession delay the buyer will give only Rs. 5 per sq.ft. which is ethically incorrect. Now I have questions for your suggestion: 1) I want the flat from the builder for my own use. Hence whether the builder can be asked to pay delayed possession interest @ 18% instead of Rs. 5 per sqft? 2) Which legal court should I to approach? i.e. consumer forum or civil court 3) The project has about 4000 buyers, but only about 200 or so are in touch in social media. About 30 persons whose possession are already due i.e. in 2014, are ready to go for a legal case against the builder on above issue. Can we go in group?