Flat Booking cancellation

Hi Team, I recently booked a unit in a ready to move/OC received apartment. I have paid the initial booking amount of 1350000 (10% of the consideration value) to the builder. Now, during booking, I told the builder that I do not have a lot of cash available with me and hence it was proposed by the builder to add stamp duty Of 6 percent to consideration value Of my flat and then they would pay the stamp duty charges. It would later be claimed by the builder from my financing bank via disbursement request. Now, government has reduced stamp duty charges by 3 percent to benefit buyers but builder has bluntly denied to pass on the benefit to me because as per them they were supposed to pay the stamp duty. However, they are ignoring the fact conveniently that consideration value of my unit was increased by 7.5 lakhs to adjust the stamp duty. So, the benefit of reduction must be passed on to me. I feel cheated and I wish to explore my options. Please advise what can I do to cancel my booking. Fortunately, I happen to have both the quotes available on my mail 1. Where stamp duty is not part of consideration value 2. Where stamp duty was added to inflate the consideration value for bank disbursement.