If your payment method is declined in the App Store or iTunes Store [or you have a billing issue with a previous purchase in the iTunes Store] - https://support.apple.com/HT203005
This is the most direct method to contact Apple for media/app/iCloud store support:
iTunes [Store] Support - Use this form for assistance with account and billing, code redemption, or purchase questions -->
https://www.apple.com/emea/support/itunes/contact.html
Use this method to get telephone support:
Contact Apple for support and service - "See a list of Apple phone numbers around the world."
https://support.apple.com/HT201232