And here comes the problem, I got the game in a humble bundle and they have this neat 'enter a mail adress and they send the link' feature. If I try to open the link I get this text:
"Gift key already used!
It looks like this gift key was already redeemed.
If you have already purchased the product, please find your key by using our order resender."

Anyway, I used the Humble Order Resender, please check again if that worked.