Delaying in possession

I have booked 1 bhk by my hard earned money in rajnagar extension Ghaziabad in Red apple homes in 2012. I was committed that i will get possession in next 3 years. At that builder did not have GDA Approval and told me that in next few days they are likely to get approval. Half approval work has done and half is left, so very soon they expect approval from GDA. But unfortunately this approval process took long time of around 2 years and they got it at the end of year 2015. But now it has been a long time since 2012 and have not started construction yet in the block in which i bought the flat. I have lost my patience now and i want to cancel my booking because builder still saying that getting possession will take next 3 years more. i have paid only around 15% amount of total coast of flat. Builder is saying that he will deduct around 20% amount by calculating the total coast of flat from 17 lacs. which comes around 1.97 lacs and i paid him only 2.15 lacs in NO EMI Till Possession Plan. where it seems that i am not going to get back any amount which i have paid. Please suggest what to do now. and is there any law for these builders?