Product Key not activated by merchant

I purchased Norton Security Deluxe from what seemed like a reputable eBay seller.  I received the retail box with card enclosed containing the product key code.  It seems to be an official product.  When I enter the product key to start my subscription, it gives a System Error.  I called Norton to see if they could help.  They told me the product key I entered was not activated by the merchant.  After a couple attempts at reaching the eBay seller, I have not received a reply.  I am beginning to believe I may be out the money I paid.  I do have the original box with the bar code and various numbers printed on it.  Is there any way of activating a product code key if it was not activated by the seller?