I I bought a credit and can not use it

If you haven't already done so follow the instructions on your screenshot and contact iTunes Support :

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

- click on your country's flag (the country where you live, 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'

What does 'bought a credit' mean, and you can't use it when/where ?