Have you even tried explaining to them about what happened? Have you actually contacted them yet?
Do you have an in app purchase that may happen automatically that you forgot about - a magazine app or newspaper app for which there are additional ongoing charges?
Use the links above provided by BT to contact support if this truly is an error.
FOR ASSISTANCE WITH ORDERS - iTUNES STORE CUSTOMER SERVICE
For assistance with billing questions or other order inquiries, please refer to our online support page by clicking here: http://www.apple.com/support/itunes/store/. If you cannot find the answers you are seeking in our robust knowledge base, you can contact us by visiting the following URL http://www.apple.com/support/itunes/store/, clicking on the appropriate Customer Service topic, then using the contact button or email form at the bottom of the page. Responses to emails will be provided as soon as possible.
Phone: 800-275-2273 How to reach a live person: Press 0 four times
Hours of Operation: Mon-Fri: 9am-5pm ET
How to report an issue with Your iTunes Store purchase
How to Get a Refund from the App Store