what if you tried doing this?
Take the gamecard, soak it, take thread and remove the sticker so u can see the code.
Then with a kitchen knife (not one that has a jagged edge, a flag kitchen knife) start scratching the code off so it doesnt look visible on the card. Then glue sticker on, and return it.
That way, when someone else purchases the gamecard, they will be like, wtf? theres not even a code.. That way, u cannot get banned.