Can I go for legal help in my case

Hi, I am from Bangalore and had booked a flat in June 2015 with a builder at HSR Layout Bangalore. It was pre-launch booking and the flat was offered for 25 Lakhs as I opted for a 50% down payment. I was away from Bangalore and had to be in my hometown for 10 months due to my Father's health issues. I tried reaching the builder company from my hometown over phone without response from them. I cam back to Bangalore recently and found that the construction has not started till now and the builder team is now saying that the project is in peak phase and construction should start anytime. When I asked in April, they said the construction will start in May and when I ask in May they said the construction will start in July and so on. I am pretty sure they are are going to keep customers money in their bank accounts, enjoying interest over it and keep on postponing the project. And If I cancel from my side, as per the DOU, they will just pay me back the amount that I paid till now without interest. If they cancel it from their side, they should pay 8% interest on my amount. As per the DOU, they did mention that if they cannot complete the project in 30 months, they will be paying me the monthly rent as per the area. But, I am more interested in getting the flat completed rather than the rent amount they are promising. Only option left for me is to cancel the flat but I will loose the interest on the investment that I have made. Is there any legal action that can be taken at this point or do we need to wait until the flat possession time that they promised? Thank You!