Air India Express — Refund Delay

I have been cancelled my wife's return flight ticket from Tiruchirapalli to Singapore, date of travel on 16 November 2014. After successful cancellation, I haven't get refund amount until now. I have been called numerous times to theirs customer service and customer support numbers from singapore, but no one can solve this issue. They keep saying that they will forward this issue to the relevant authority and I am being asked call them back 2 or 3 days later. When I am calling again, they are saying the same. I am fed up of choosing this ******* airline. I had sent so many emails with attached copy of my PNR PV7EI1 also couldn't get a single reply from theirs side. Please help me out this issue.