The Sims Medieval Limited Edition Content Code

@CMeki, I was hoping an EA employee would chime in, but your snide response leads me to believe they don't do that.
I found the box in my storage unit which contained my code. I entered it in and voilà, it worked just as customer service said it would not. Surprise, surprise.

Moral of the story: don't rely on EA customer service to help you if you have a problem. They created a separate forum where players do the work for them.

For other people having this issue in the future, here is a helpful response: since I was able to reenter my same Limited Edition Content Code after they swapped out my CD Key twice, I'm guessing these promo codes are resusable. If you can't find yours then you could probably ask a friend or do some digging online. The best thing to do preemptively is to save your code in a document and back it up to the cloud so if you do have trouble finding it in the future, you won't have to go through the hassle I went through just to get nowhere.