purchase history

I see a charge on my account that I did not make

You've checked your purchase history to see what it's for ? If you didn't make the purchase, and nobody else has access to your account or devices and made it, 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