Re: code already redeemed
If the code has already been redeemed, it should be taken back to the store where you purchased it, it's possible they accepted the game as a return after the original purchaser already redeemed it, or someone just stole the code from the box and returned the items to the box on the shelf.
If it's not already the version you have, I'd suggest getting the Game of the Year edition when you exchange/return the faulty copy you have, as it contains all the extra content (DLC) at a much cheaper price than buying it separately. It's also possible to purchase the game online as a digital download, no box or packaging, you can download the game and be on your way.
Dragon Age Inquisition is a single player game, but it does have (completely ignorable) multiplayer, which means extra security. You can play offline, after you initially authorise and DLC with the servers.
Having the game linked to your Origin account means that, should you ever lose the code or physical copy, it won't matter, as it will still be in your Origin library (as long as you don't forget your Origin account details, of course). Just make sure to change your Origin settings to suit you (for instance, it will default to starting when you start your computer, you can turn that off), and Origin shouldn't be too much of an intrusion. I think pretty much all EA games require it these days (unless you get them through Steam... which requires Steam instead).
Hope that was of some help. I miss the days of 'insert disk/CD/DVD, install and play', too. Although I don't miss having a million game boxes everywhere. 😛
