iTunes charging my credit card when I had money left over from redeeming a gift card?

All right, so a few days ago I went to Walgreens and bought a $30.00 iTunes gift card for myself. I never use my actual credit card to buy music; I always buy gift cards to purchase them, however I have put my credit card number in my account info once to pay for an outstanding balance. After I bought this gift card, I immeidtaley redeemed it and began buying songs, and everything was fine. I got what I wanted, and when I was done I had around eight bucks or so left. So just now, I tried to get another song, and iTunes brought me to my payment info, which, strangely, has my credit card informatio set in it when I had previously selected it to say "NONE" when it asks for credit card info. Not only that, iTunes is telling me that my card is declined.

When I looked on my phone to see the activity of my card, I saw the $30.00 purchse I'd made at Walgreens, but there was also an 11 dollars that iTunes charged to MY account when they should've taken it off the gift card. Why is that? Why have they put my credit card info back into my account when I specifically selected that I wanted NONE. I'm pretty ******.