1) how can broker submit application form without your signature? why did you not sign the agreement for sale ?
2) i do hope you have made payments by cheque and have receipts for payments made by you
3)if you are not in position to make further payments and want a refund of payments made by you send a letter to builder informing him of your inability to make further payment and request him to refund the amount of Rs 15.50 lakhs paid by you as you dont want to purchase the flat
4) if builder refuses to refund move consumer forum against the builder for deficency in service and seek refund with interest .
5) contact a local lawyer