Why my credit card was declined if its ok?

These are user-to-user forums, nobody on here will know.

Is the credit card registered to exactly the same name and address (format and spacing) as you have on your iTunes account ? If it is then you can contact iTunes support via this page and see if they can help : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption