Related to Refund of Advance money

Please advice/support for the below situation. I have booked a flat paying Rs.5 lacs to a builder, i was given a time of 60days to pay the half balance amount around more 15 lacs. But after giving the 5 lacs cheque within 15 days i told the builder person that due to my personal problem i cant afford this deal as i need to wait for 5 years as this is a pre launch project so please cancel this deal & return my money 5 lacs. At the time of taking cheque the builder person have said facely that no need to worry for return money as u need to cancel u may proceed & will pay your complete 5 lacs back to you at earliest within some days. But now that same person have stop attending my calls & when i contacted the builder office i was been told that the person is busy in visiting site projects & second day i was told that the person have left the job & we no more know that person & also clearly ignore me to give that person contact details. I have been told that from your 5 lacs 50k will get deducted & u will be give 6month post dated cheque. When i explain my needs & condition to them they told we will deduct 25k but the cheque will be 6month post dated given to you. I can't afford & think that even 25k should be deducted just for within 10days i told them i need my money back but the builder person ignore & extended it for more than 1 month & escape without contacting me. Please advice/support for the above query. Sorry for typing such big paragraph but need a strong advice in this situation were to go whose help can be taken as this is completely fraud done with me.