Anyone here ever use trade credit via Gamestop.com?

So here is the deal.... I had two cards with trade credit amounting to little over $30 so I figured I would order Hitman Absolution for next week. I applied the credit it showed the discounted price with my one day shipping ended up at about $42. That was the total it showed when I hit the final button in the transaction. So I looked at my invoice today and it showed a total of $74 which would have been the normal price. I went on the website and checked the balance of both trade credit cards and the site said they were both at $0. So....I dunno If I should be worried or not about getting charged full price.