I have the very same problem. I made the Rs. 5000 purchase only for the 15% discount to buy a phone as a birthday gift on the 25th. I still havent received the coupon, today being the 29th!
I have had a similar problem with eBay before and they dont seem to have the resources to keep up with their promises. I had made a purchase of >8000 to get a free Skullcandy Uprock Headphone. The product didnt arrive for more than 2 months and after repeated pestering and inquiries, they gave me a flat Rs. 1400 voucher, when the cheapest new Skullcandy headphone costed Rs. 1600.
eBay's reputation is maintained only because of their sellers. When eBay needs to offer discounts or free gifts they always default on it.
Please don't ruin your reputation with this and email the vouchers at the soonest!