Builder delaying giving possession of property

I bought one property in Bangalore in Aug 2013 and agreement was that it will be completed in 15 months with a grace of 3 months, so basically flat was to be handed by March 2015. Since it wasn't mentioned in contract, I got an email by them saying that they would have to penalty of 15,000 pm until they hand over the property. I was outside India that time but planned to come in June and they agreed on that. I came spending money but was shocked to see that it wasn't complete, so I had to return back once again. I finally came back in August 2016 but even then it wasn't completed. I stayed in one room from Sept-Nov to make sure that construction is completed but even then they didn't complete. They didn't give permanent meter but gave temporary electricity from somewhere. I had to move to Chennai in Dec & I travel every weekend but still facing same issue. And now that I ask them to complete, they always say that 10 - 15 days. Please guide.