bank loan for the flat purchase got delayed than the agreement time. So seller refusing to sell the

Dear sir /madam. We have made a decision to buy a resale flat from the seller. While negotionating on price,he has made lot of promises that he will support us in documentation .he is convinced us in a pleasant manner to close the deal early . By trusting his behavior we believed him and agreed to purchase it. He also mentioned that pay the advance early and will wait till get the bank loan for the remaining amount.he assured to wait till get the loan.but formally we have mentioned 45days as agreement validity with the legal adviser suggestions. We trusted his word and paid the advance of 18lakhs to him. Unfortunately our loan got rejected in a bank after 45 to 50days of processing time. So we have applied to another bank and they are ready to give. But now our seller changed his commitment and saying that our agreement time is expired and we are not eligible to proceed for the loan. And he also not willing to refund our advance money. What to do now. We are really helpless.