Builder malpractice

1. Is the builder buyer agreement the last word or is there any consumer protection law above it. In my case the Builder is paying delay penalty starting from the time it was asked for via mail by the buyer till 6-7 months prior to work completion. This he is adjusting at the time of final demand notice with 0% interest. For their own money they charge 18% interest. As it is they pay only Rs. 5/- psft. Can I claim 18% interest on it and demand it starting from delay date till possession date ? Though the builder buyer agreement says it will start from when I claim it. 2. They are charging interest on back dated demand notices. They have the practise of sending back dated demand notices and charging for even more no. Of days than their own back date. They have very conviniently used a courier service which does not stamp the date on envelopes while sending. How can I claim back this amount? 3. They have been fleecing money for increasing super area which is a malpractice. They don't respond to any query regarding proof of increasing the area. With each upcoming tower they are charging more and more in lacs for nothing. They have not shared their Floor area ratio or anything which determines the increase in super area even after 6 months of buyers asking them. They just don't respond to such things. How can I claim this money back?