So, as the title says, I bought used copy of Diablo 3 Ultimate Evil Edition: Reaper of Souls Expansion and I really need a Game Key. But I'm not sure how to acquire one other than buying an entirely new copy, but I think it'd be rediculous so sell back my copy for $18 when I literally just bought it for $55 just so that I can purchase it with the Game Key..

Could anyone let me know something?