No refund from builder for cancellation of flat

In the year 2011 I paid Rs.8.5 lakh as advance for a flat of Builder in Kochi. I dropped the plan because of my financial difficulties. The builder sold the flat to another customer. For last 4 years I am asking for the refund of my payments. The original documents demanded by the builder to prepare for refund. and so far no payments received and the original documents are with the builder. By contacting by telephone. the reply is next week- month- and so on for 4 years. How can I get the money from the builder? Can you help me?