Payment

You can try contacting iTunes Support for assistance. There were multiple posts yesterday about people having problems with their payment method. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option. 

iTunes Support

iTunes Support – world wide

Do you have another card that you could try ?

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, and have been issued by a bank in the country where you live (and therefore the country which is on your iTunes account).

If the card isn't accepted by iTunes (I assume you've tried adding it on both your phone and computer's iTunes), and if you don't have another card (some debit cards also work with iTunes), are iTunes gift cards available in your country ? If they are you might be able to use them as your payment method.