Consumer Redressal

I have taken a gift coupon for INR 5000 from Zara, a global clothing chain. I did not know that it has expiry date, which is written on back of the card. Surprisingly there is no issue date on the card. My card expired as I did not use it in stipulated time and the company refuses to revaldiate it. It is almost taking away my cash and not letting me use it later. When I contacted them, they flatly refused. Pls help.