I Tried To Redeem A MS Point Code On Xbox LIVE And It Didn't Work?

I searched all over www.xbox.com/support, called their 1-800 number, and even sent them an email, so far, no answers. So the last thing I can think to do is turn to Yahoo Answers! Well I bought a 1600 MS Point code from gamestop.com, and chose to have it delivered digitally, and when I went to redeem it, it didn't work. It says its not a valid code. What should I do to get a refund/free code from Xbox/Gamestop? And don't say to go to those MSPoint generators, those are all scams filled with viruses and false promises. Help?