Not returning token advance

In 2014 Nov I have bought a flat through Home Loan near MUMBAI. After doing the registration of property in my name only we get to know that Mother Document is missing for that property, Due to that home Loan get cancelled. Since from 7 months I am pushing the Owner to do cancellation of deed and getting only token advance (Registration Fees and token advance get refunded) that I paid. He is not responding to that. Now he rented that flat also. We pushed him a lot for doing cancellation of deed,he was telling within 10 days,every time by saying some execuses he is extending the cancellation. but now he had sent one legal notice states that we have not given the balance amount to the Seller after doing registartion and asking as to do the settlement of remaing amount to take the possession of the Flat.Also while giving token advance we have signed a doucment ,that tells as if this transaction not happend within 15 days ,the amount paid will not be refunded.The seller is a very big Fraud.what we have to do next?please give suggestion.