Refund of booking amount paid during prelaunch phase of apartment

I have booked a flat during prelaunch offer by a reputed builder in Bangalore. Within 3 weeks of booking, even before the launch of the project I requested to cancel my booking and refund the booking amount. This request was sent through an email to the sales representative. Sales representative presented the case before the Sales head and the reply from sales head and the management is that cancellation is not possible now. I have got the receipt for the booking amount and the allotment letter for the unit. As per the terms and conditions of the Application Form, "Allotment letter is the provisional allotment letter and will be final only after the applicant executes the S&C agreement". There is also a clause for cancellation which says "Cancellation will be excepted only in exceptional cases and at the sole discretion of the developer" "If cancellation is accepted by the developer then applicant has to be pay 25% of the agreement values plus legal fees and taxes if any" After reading all these clauses it seems its completely favouring the developer and no choice is given to the consumer at all. I would request legal experts to provide their opinion on this matter. I don't want to go ahead with the investment and would want to get back by booking amount. Thanks SK