Q: Why have I been extra charged for an app and have been billed twice for the same app?

We are are fellow users here on these forums, you're not talking to iTunes Support here, we won't know why.

I don't know what you mean by 'extra charged' (have you made in-app purchases within the app, or are you in the US and need to add on your state's sales tax to the listed price ?), or have you added or changed your credit card details on your iTunes account ? If you have then each time that you do so a small temporary store holding charge may be applied to check that the card details are correct and valid and that it's registered to exactly the same name and address as on your iTunes account - it should disappear off your account within a few days or so.

Store holding charge : http://support.apple.com/kb/HT3702

If you've been double-charged then try the 'report a problem' page to contact iTunes Support : http://reportaproblem.apple.com .

If the 'report a problem' link doesn't work then you can try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption