Trouble for billing

What happens when you try to add your details (if you are getting an error message then what does it say ?), and what are you trying to use as your payment method, credit card, debit card ... ? If it's a debit card then they no longer seem to be accepted in all countries, and even where they are it seems that not all work.

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 and your iTunes account are.