Q: Hello,  loaded a iTunes card a couple days ago, and purchased a book on iBooks.  I would like to use the remaining balance to purchase another book however it keeps saying my purchase is declined as my credit card is no longer in use.  Any advice?

Hi Mskvns,
 

Thanks for visiting Apple Support Communities.
 

I see you want to buy an iBook with your remaining iTunes Store balance, but the purchase is declined.
 

It sounds like the gift card balance isn't enough to cover the cost of the book, and you don't have a valid payment method on file to pay for the remainder. If so, you just need to update your payment method using the steps in Change or remove your Apple ID payment information.
 

If you already have a valid payment method on file, try the steps in If your credit card company's records don't match your records in the iTunes Store.
 

Best Regards.