there was another giveaway for this recently that was - by the giveaway creator's own admission - not actually for this; noting the coincidence - and with no accusation - i simply say thanks for giving this Neil Dragon Pack DLC for the free-to-play game Time of Dragons
and link to the FAQ and Guidelines since this is your first giveaway

Hi! I won this giveaway, but i can't to activate this. Therefore I refuse this gift. Thanks

Hi. I can't activate this key. It says I already own it, but I don't own the dlc.

I already own it. And by the way you can't just change it. You should have check the game key in the first place.