Runwal Group — Fungible FSI

I have bought 2.5 BHK in Rosewood in 2010 and was charged for 1300 saleable area. Agreement for sale was executed in 2012 stating only carpet area 787 sq.ft. I received a letter in July-2015 from the builder asking to pay for the increase in carpet area 138 sq.ft extra because of Fungible FSI. They have already charged me on super built-up area of 1300 which includes the utility+flower+deck area and now charging me again? This is totally unacceptable and a deliberate attempt to collect extra amount from genuine customers. Be aware while dealing with builders who are not professional and delay possession only to gain for their profit in finding ways to overcharge the customers.