These are user-to-user forums, we won't know why your payment method is being declined.
Is the namd and address on your credit card exactly the same as on your iTunes account ? If it is then you could try contacting iTunes support and see if they can explain why (it might be your bank that is declining it) : 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
This site contains user submitted content, comments and opinions and is for informational purposes only.
Apple disclaims any and all liability for the acts, omissions and conduct of any third parties in connection with or related to your use of the site.