I got an itunes gift card on Jan. 28th and it was scanned into my iphone. On Jan. 29th I rented a movie through itunes on my macbook pro and my credit card's being billed for it. How do I get it to deduct my purchases from the $15 credit (which shows at the top of the itunes screen on my Macbook)? FYI, I have an iphone 5s and 0S X Mavericks on my Mac, and I'm running itunes 11.1.4.