[Resolved]  Builder — demanding more money after giving possession

We got ourselves a flat in a society.After giving the complete possession 2-3 years back, the builder is demanding more money on the basis that land rates have increased. Many others who bought flats in the society have paid earlier the amount of 1-2 lakhs extra. I would like to know whether it is possible for a builder to demand more money on such grounds after giving the complete possession. If yes then on what grounds. And if no, then what can be done to negate this claim of his.