My complaint is against the builders of my newly purchased flat. The problem is that the carpet area

My complaint is against the builders of my newly purchased flat. The problem is that the carpet area of the flat is less than the area promised by the builders. After the continuous and long discussions for 6 months and after measuring the carpet area 5-6 times , the builders at first place agreed to pay me the compensation in the way that they will get the interior wood work done from there own and adjusting the less carpet area amount in the wood work. But after the wood work is done, the builders are now refusing to adjust the whole amount .. they are saying that they'll just pay the half amount i.e. Rs. 27000 (half payment). After this I told them that i'll take necessary actions against them; they mentioned after this that they'll not pay a single penny now.

Please suggest me that do i hold a valid case against them or not and if yes then how do i proceed with the case.