iTunes card

Today I just bought iTunes card ( $50 ), once I redeem it by taking the picture of the code, it was correct and I was waiting for the $50 to be in my iTunes store account. But the page was not loading and then is shutdown. I re-open iTunes store and check my balance and it was the same ( $0.84). I tried to use the code again to redeem it because the first time it was not success. But once I write the code, a message appears (The code have been used already). So, what should I do?