Procedure to cancel apartment booking with builder

I booked an apartment in Godrej 101, Gurgaon two year ago. I have signed the apartment buyer’s agreement and already paid 80% cost of property. I now wish to cancel the booking. Godrej have provided the cancellation quote in which they are charging penalty of 20% cost of property + GTS of 20% cost of property + all taxes paid till date. I have read the apartment buyers agreement in detail and cannot find any clause related to “cancellation of booking by buyer”. The only clause mentioned is in the event of default of payment by the buyer, the builder will terminate the agreement and charge 20% cost of property. My question is – as no clause of “cancellation of booking by buyer” is mentioned, Godrej should not charge any cancellation fee (except taxes) or can Godrej charge 20% cost of property? I have not defaulted on any payments till date.