Escalation of Cost of dwelling unit(flat) & delay by builder

I booked a dwelling unit(flat) in 2008 with Air Force Naval Housing Board a welfare venture managed by Indian Air Force. As per terms and contract, the total cost was then fixed at the cost of Rs. 21 Lakh. There after I projected for minor modifications in which it was told to pay another Rs.67,800/- which I agreed to pay AFNHB . The builder was supposed to hand over the flat in 2014. Till date, the project is still going on and likely to complete after one year or so. Problem comes here that without handing over the flat builder has increased another Rs.9 lakh. Till date I have already paid Rs.21/- whenever I am supposed to as per the date without any delay.Will someone guide me whether I should file a legal notice or to approach RERA. Which way and where would I approach to get my flat early and without any cost increased.