If you can use the game but can't unlock promo, bundle or DLC here's a easy solution.

If you have a gamesas account linked with your game don't use any other accounts. It's because of license agreements and protecting from hackers and piracy.

Link : http://www.gamesas.com/redeemcode

Yeah. That's the link the currently prompts me to sign in, even though I'm already signed in. ^-^

Same thing happens to me.

Are you doing it from in-game or the web.
What ever you do use the account associated with your game.