I'm sorry but if the card is refused you will have to contact the credit card provider. We cannot help you with that.
The only accepted methods of payment follow.
WordPress.com uses PayPal as the payment processor, and as such, can only accept payment from countries they support: https://www.paypal.com/worldwide/
In addition to major credit cards Mastercard, VISA, American Express, Discover, and PayPal https://www.paypal.com/worldwide/ WordPress.com can accept echecks and some debit cards.
The debit card must have a VISA or Mastercard symbol on it, and should work just like a credit card when selecting the VISA or Mastercard option on the payment form, even though it's a debit card.
More about echecks here:
WordPress.com also accept Bitcoin for payment of certain upgrades ( bitcoin cannot be used for domain and premium theme purchases) - you can learn more here: http://en.blog.wordpress.com/2012/11/15/pay-another-way-bitcoin/