Just look at Mountain Lion in the App store - the purchase has changed to download. Your code worked.
If you did the uptodate and got a redeem code - and it says its already been used, just go back out and click on Mountain Lion, and you'll see the Purchase icon has changed to a Download icon. the code was accepted so fast, that when you clicked submit, it tried to submit again, and I'm downloading now.
Did you actually receive your e-mail yet though? I submitted mine over an hour ago and no e-mail yet.![]()
WORKING!
Finally!!!! (here in the UK)