Refund of paid money by builder on cancellations of booked r

I have booked room two years back which was under construction by paying 20%(2lakh) of total amount. While booking builder had given only recipiet for payed 20% amount. Now flat is ready and we planned to pay total amount with legal registration process. Now builder refuse to do legal registration process and offering us to do register by notary only stating that flat belongs to me. As its seems some illegal happening over here we have cancelled booking and request him to repay back paid 20%. Builder has given us two cheque and told us depoist but when deposited that cheque it got bounced due less balance. Now builder is not responding properly and failing to repay. Please let us know legal way to get back money. Thanks in advance.