Consumer Fraud Case

There are two parties involved here, one 3rd party agency though which I booked a property and other a builder in which a property was booked. I booked the property but I've never received a builder buyer agreement. The property was booked under 10:80:10 payment scheme. I paid initial 10% of the property. Next steps were for bank to process the loan and builder to share the agreement. Both of the things never happened as IndiaBulls didn't process the loan due to IL&FS crisis or so was I told. Then we approached HDFC bank for loan processing but it also didn't go though as government by then had cancelled the 10:80:10 scheme. I was later advised by the third party agency that I should cancel my booking and ask for refund. I've already submitted the request in last May and it was said by builder that they would refund the amount deducting the GST. But only after delaying it consistently and asking for documents, they require more time to process the refund which has been going on for more than 8 months, now they are saying that they would not refund any amount and asking for more money to be paid to continue with the unit booked. Please advise as to what can I do in such a case.