Cancellation Of Affordable Housing Flat Booking

#I have booked a flat from Signature Global in Project THE ROSELIA SECTOR 95A, under affordable housing scheme in April -2019 under my wife Name Mrs. Neha Jain and deposited 5% booking amount to builder Rs. 104852. #After Draw on 20th June 2019 a unit in G Tower flat no 807 was allotted to us. #Due to Some issue i want to cancel the booking and submitted the cancellation request to builder. #Cancellation deduction policy at the time of booking is as per Affordable Housing Policy(NO. PF-27/48921(released on Aug 13) and we have to bear deduction of Rs. 25000 at cancellation(Same was mentioned in Application Form which was signed by us at the time of booking) #But now builder imposing deduction as per revised affordable hosing policy ( NO. PF-27/15922 ) which was revised and effective from 5th July Onwards. Deduction as per revised policy will be Rs 25000+5%of Flat cost which comes approx Rs 153000. Kindly suggest How to fight against builder legally