Delayed construction and possession and unfair refund policy

I have booked a flat under the project (emerald floors premier phase 2, golf course extn. road, sector 65, gurgaon)in 2010. The due date for possession was 2013 june sometime. Now it is 2015 and there is no sign of further construction. The construction has stopped since last 10 months and i dont know when the construction will start. I have invested a big sum of my hard earned money into this flat. I have been calling them since more than 10 mths and every time the customer service say that the construction will start in 2 months but it does not start. Now when i went to gurgaon to meet their senior officials in their sales office in Sikanderpur office in gurgaon, they gave the same excuse again stating that the construction will start in 2 mths. When i asked for the refund, they said that i can get a refund post deducting 15% and other charges from the total amount i have paid. In fact i should be getting the entire amount i paid along with EDC, IDC charges and also an intrest amount on the sum paid rather than any deduction because it is their fault that the constuction has got delayed by 2 years and there could be a further delay of 2 years if the construction starts now.The total delay is estimated to be 4 years which is unacceptable. i have never seen such unprofessional builders. Pl. help me get my money in full with intrest.