Delay in possession

Sir , My name is sreerag, i looking for a kind advise against the builder due to the Late of handover of the projects. I book this Flat on Chennai on 2013 (Puravankara builder). the project completion time suppose to be early of 2015. and regarding the payment 86% of amount already 10% advance +76% bank loan) On 2015 they revised there schedule 2 times, as per the second revision they need to hand over the flat by December 31st 2015) still this not happened. From the September 2015 construction status is more than 85 % . from September itself we are asking the permission to allow us to start the interior work on apartment, but they are not allowing those kind of activities due to safty/damage and various reasons. And also my parent who is staying in Coimbatore in a rent house (which is paid monthly Rent 3000 Rs/)also contract expired on last june. and now i am renting a house for them monthly 12000/Rs) due to the late handover of this builder. In the above situation what action i can take against them. Expecting your kind Advise Regards Sreerag Srgmohan@gmail.com