I've investigated the situation and it turns out I've accidentally missed the fact that the key in question was already given out in another giveaway roughly one year ago, which I've somehow forgotten to update. I don't know how it happened since I'm pretty sure I did a check before posting the giveaway.
I would like to request your permission to delete the giveaway. Alternatively I can try to get you another key but it might take quite a while. Sorry for the issue.