I purchased a game serial code, but it does not appear in my library

I purchased and registered a code today, but I’m getting a "Code already used" message, and the game isn't showing up in my library. Is there any way to resolve this? I'm having trouble communicating with customer support due to the language barrier. I’ve already tried clearing the cache, logging out, and restarting the app. The serial code I bought was [definitely] for the full game!!