Q: I didn't purchase anything

Where are you seeing this billing? If you received an email about purchasing something, it could be a phishing attempt to get your Apple ID information. If it appears on your credit card bill, then check your iTunes account Purchases section. If you have a question, contact iTunes support. https://www.apple.com/emea/support/itunes/contact.html

First make sure it is an official message (if  it was an email): Identifying legitimate emails from the iTunes Store - Apple Support  and iTunes Store charges on credit and debit card statements - Apple Support

If it is real, see here: Report a Problem and If you think your Apple ID has been compromised - Apple Support

-AJ

Go to http://reportaproblem.apple.com and see what exactly was purchased if anything.

If no unknown purchases appear there, the e-mail you received was likely a phishing attempt and can be ignored.