If you hadn't redeemed the card onto your account when you did the purchase then your bank card will have been charged - if there was/is insufficient money in your bank to cover the charge and you've since redeemed the gift card then it might now have been charged to that.
You can view your purchase history via your computer's iTunes to see how much your purchases were : See your purchase history in the iTunes Store - Apple Support
Or one your iPhone you can view the last 90 days purchases via http://reportaproblem.apple.com
You should also receive an emailed receipt listing the purchases.
Both on your computer's iTunes and the emailed receipt should be how the purchases were charged e.g. 'store credit' if using your account's balance, though I'm not sure what that will show in your case.