Q: Credit card decline

In countries where the iTunes Store only sells apps, the accepted payment methods are Visa, MasterCard, and American Express. Other payment types such as gift cards, store credit, and PayPal aren't accepted. Depending on your App Store country, prices might be listed in your local currency, US Dollars, or Euros.

Payment methods that you can use in the iTunes Store, App Store, and iBooks Store - Apple Support

Change or remove your Apple ID payment information - Apple Support

They are proper credit cards, not prepaid cards or debit cards ? For a card to have a chance of being accepted it needs to be registered to the same name and address (including format and spacing etc) that you have on your iTunes account (so prepaid cards will tend to not work), and have been issued by a bank in the country where you are (and therefore the country which is on your iTunes account). You've checked with the card issuers in case they are declining them for use with iTunes ?