The code I had wasn't registering on the website, so I sent General Mills a quick email stating it wasn't working. Honestly, I wasn't expecting much in return - probably a 'well go buy another box' response.
They emailed me back within a day, and gave me a replacement code. Which worked! No questions asked, no insinuating that I was lying. Just a replacement code.
It honestly wouldn't have been an issue had my son not wanted it so badly. Now, he can have his shirt, and wear it with pride!
Thank you, General Mills!