Indigo Airlines — NOT REFUNDING for my tickets, which they did not indicate as non refundable

Address: Mumbai City, Maharashtra

Hi, I had booked a round trip from Mumbai to Bangalore ticket on April 1st, 2015 from a guest login of the indigo site : https://book.goindigo.in/ Due to some reason I have to cancel my travel so I called customer care to cancel my tickets. They are telling me that my tickets are non refundable... When I was booking ticket I was knowing that I may have to cancel my trip so I checked for changes and refundable and then booked my tickets. Ticket Reference No. M9F98T And now they tell me its not refundable. I mean how is it possible. Its a matter of 4000 rupees and I want u to look at this and refund me my money.