We are fellow users here on these forums, you're not talking to iTunes Support nor Apple.
Do you have an iTunes account ? If you do then if you log into the account on your computer's iTunes via the Store > View Account menu option you should then see a Purchase History section with a 'see all' link to the right of it. Click on that and you should then see a list of the purchases on the account.
Viewing purchase history : http://support.apple.com/kb/HT2727
If it's a frequent payment then you may have an auto-renewing subscription - there are instructions on this page for managing and stopping them : http://support.apple.com/kb/HT4098
If you don't recognise the charge or you can't find it then you can contact iTunes Support via this link and see if they can help : 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