Cancellation of Flat booking

Hi sir I have booked a flat in pre lunched project in Oct 2015, for this I have provided the booking amount of Rs. 100000. The builder have provided the receipt for the same mentioning on receipt Interest free Refundable amount. Initially was able pay agreement value and other fees, so I had requested the builder for agreement and registration, but project wad not sanctioned at that time . When the project sanctioned in May 2016 then builder called me for registration and agreement, but that time I was not able to pay the respective fee due to some unavoidable reason. Builder has forced for either go through agreement or Cancellation. I had requested for three months period to pay but they denied. finally I had canceled the booking and send a letter for cancellation of booking and return pay the booking amount of Rs. 100000. Now builder says that the cancellation amount of Rs. 50000 will be reduced from your booking amount So some one Please advice me for the problem and what further action should be taken Thanking You