My VISA (NationHela) Card has been declined from registration, where is the problem?

What sort of visa card is it, debit or credit ? If it's a debit card then I don't think that they are still accepted as a valid payment method - they are not listed on this page and there have been a number of posts recently about them being declined

If it's a credit card then is it registered to exactly the same name and address (including format and spacing etc) that you have on your iTunes account, it was issued by a bank in your country and you are currently in that country ? If it is then you could check with the card issuer to see if it's them that are declining it, and if not then try contacting iTunes support and see if they know why it's being declined : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Account Management

This would be something you really need to contact Apple about at the link King_Penguin posted. There really is no way for any of us here to know why a particular person's payment was declined.

BTW, just because the issuer says it is accepted worldwide, does not compel any given vendor to accept it. Individual companies or retailers can make their own decisions about what payment is acceptable or not. In the USA for example, there is in fact no law that compels a company to accept cash, for example, and a company can legally refuse cash as a method of payment, just as they can refuse any particular credit card.

Is it registered to your name and address that you have on your account ? If not then it will fail that part of the iTunes validation.

Does the card have funds preloaded on it? I've seen posts here of people who tried putting a pre-paid card on thier account before they had put funds on the card, and it was refused. I believe that was due to the initial authorization hold being refused due to insufficient funds, so the card could not be verified.

If it says that you need to "contact iTunes Store Support to complete the transaction," then you need to contact iTunes Store Support. If it says it doesn't match bank records, was declined, or the security code is invalid, then you need to contact the credit card issuer.

You also shouldn't use prepaid cards with iTunes. If all you have is a prepaid credit card, you should use the prepaid card to purchase an iTunes Gift Card and redeem that to your account instead. Debit cards issued by banks with accepted credit card logos on them, accepted credit cards (non-prepaid), accepted pay services, and iTunes Gift Cards are what you should be using.