Unknown billing

Does it contain your billing address from your iTunes account and is grammatical ? To check an email :

Phishing and similar emails : Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

Genuine iTunes emails : Identifying legitimate emails from the iTunes Store - Apple Support

It very likely is a scam or phishing attempt.

Read here: Identify legitimate emails from the App Store or iTunes Store - Apple Support

and

here: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

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.

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