Refund of Booking Amount

Hello Sir/ Madam. I had done a booking in one of the under construction project in Thane. As I has planned to sell my other apartment in order to continue with this project, however I was not able to sell my other apartment so I requested to cancel my booking to the builder for which I had sent a email for cancellation as requested by builder. The Builder is now saying that you have signed the booking form which has a clause that 5% of the amount will be deducted of the total flat cost. I am not having a copy of the booking form to check as we had just paid the cheque and signed the form at builder office and no copy of booking form was given. I am stuck now for last 6 month I am sending email to refund and the builder is saying we will refund only if we are able to sell the flat. I have paid Rs 5 Lac as booking amount. Please let me know how can I get the booking amount from builder. Some people are saying if you register the flat/ allotment letter is given then only the builder can deduct the money in my case no agreement or allotment letter was given. Please provide guidance for the above issue. thank you.