Refund of Service Tax and Cancellation charges

In 2016, I have booked a flat by paying Rs. 1lakh with the verbal confirmation saying that there will not be any cancellation charges or any other hidden charge, when visited the bank for loan, we got to know that this flat is already sold to another customer, we asked clarifications as usual got irrelevant answers then as per recommendation booked another flat with same builder and asked for all the given confirmations on paper but they said it will be mentioned in the agreement copy. I have asked a sample agreement copy but they said will provide and made us to pay total Rs. 4,00,000/- and then we received the sample agreement copy but as promised the possession and other clauses were neither informed not acceptable, then because loss of trust and misleading information, I got tired and decided to cancel the booking, when we informed about cancellation, they purposely paid the stamp duty very same day. I have got the stamp duty back after finishing government procedure. I have not signed agreement of sale, but they have forcefully taken a signature on the letterhead saying that, we will not claim anything against this property and said us if you do not sign the letter, you will not get your balance 75,000/-. After signature only they have given 75000/- cheque. So, total they have deducted Rs. 40,000/- means 25000/- cancellation with 15000/- Service tax. As the sale agreement is not signed, is builder have authority to deduct cancellation charges - As they have lied from the beginning and did not informed us anything during the booking and Service Tax, How to get cancellation charges and service tax refund. Please advice.