Have you actually been charged? Have you checked your Purchases history? Are you sure the message is legitimate? Does it contain a link for you to sign in somewhere? It may be a scam.
Apple will always address you by your name or the name they have on file for you and the e-mail will be from @apple.com or @iTunes.com. E-mail addresses can be spoofed. You can go to Mail/View/Message/Show all Headers to see more.
Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams
Identifying legitimate emails from the iTunes Store
Send the e-mail to Apple as an attachment to a new e-mail before deleting it. You can forward as an attachment by going to Mail/Message/Forward as attachment.
reportphishing@apple.com
Purchases - Hiding/Unhiding
If necessary, there is a contact link.
Apple ID Support
Apple Support by e-mail or chat Select your device, Battery, Power and Charging, then Power adapter not working to get a chat option. If the initial contact can’t help you, ask them to have someone who can help contact you. If you need to talk to them, ask them if they will do a Skype or FaceTime with you.
Or fill out and submit this form.