Nomnation Charge Fees Changed on Re-Resale

I booked a flat in Kolkata in Resale. The person had to give the builder Rs.50/- per square foot as nomination charge. I was told that if I resale this flat to someone I will have to pay the same fee Rs.50/- per square foot as the rules for nomination cannot be changed after the flat is booked. However today (after 2 years), when I wanted to nominate someone for the flat, the builder is asking Rs. 250/- per per square foot to nominate. Please note that in the terms or resale, the charges of nomination was not mentioned. It was written "as per the application". However even in the application it was not mentioned. So my question is: Is it legal or illegal for the builder to change nomination fees as per his will? Please note that No Nomination Charges are mentioned in the sale agreement except nomination fees will be "as per the application". However there was no notation fees mentioned in the application when I bought the flat on resale. So the question is - in my case is the builder charging me legally or illegally? Do builders have the right Not to mention any nomination charges in the terms yet charge anything they want on nomination?