LoL pre-paid riot points card won't work in store

I recently purchased a riot points pre-paid game card from gamestop. However, when I enter the code in the store it continues to say an error has occured. I am not sure if it used my code or not however, I have not received the credit in my account. I am assuming it is just a bug within the store seeing as how it has been having a few issues today. Please fix. :)