Buy something in a app

If you haven't already done so you should contact iTunes Support as instructed by the message (these are user forums, not iTunes Support) :

- go to http://www.apple.com/support/itunes/ww

- click on your country's flag (the country where you are, and which is therefore the country on your account)

- click on Contact Support towards the top right

- click on Get Help under 'Talk To Us'

Or use this form : https://www.apple.com/emea/support/itunes/contact.html

Difficult to say if anybody on here can help you as you haven't given any information about the problem. What happened when you tried to buy the item ? If you got an error message what did it say ?