In fairness to the OP, it is ludicrous that anyone would sell a used game knowing that whoever purchased it would be unable to use it. That's like those people who sold empty Wii boxes on eBay; sure, you're "technically" getting a copy of Battlefield 3, but you bought expecting to be able to play it, not just look at the disc.
In fairness to Amazon, I'm almost positive they don't sell used games and you were going through a third party seller. While it is shady, it is not really Amazon's fault. I mean, yes, they should thoroughly vet all third party sellers to keep these shady business practices out of it, but there are a lot of people who don't know how DRM works who won't realize that a used EA game is worth less than a brick.
Lesson learned, hopefully.