Hello heathad,
I am sure you are eager to watch Django Unchained, and I would be concerned too if I didn't see it downloading after entering the authorization code. It sounds like you have already associated it with your account since you are being told that the code has already been redeemed. I found an article with steps to download past purchases from iTunes:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
http://support.apple.com/kb/ht2519
Follow the steps listed under the respective device that you are trying to get the movie downloaded to. Happy watching!
All the best,
Sheila M.