I got an email saying that I purchased an item that I did not purchase

Check:

See your purchase history for the App Store or iTunes Store - Apple Support

To see if it was a purchase on your account.

Also take a look at these articles

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

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

You can report it by forwarding it to reportphishing@apple.com.

Hope this helps!

Has your credit card been charged? 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, not Dear Customer, Dear Client or by using your e-mail address.  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. Apple emails won't have poor grammar/misspellings. Apple e-mails will never contain an attachment. Apple will never request personal information by email such as Social Security numbers, your Mother’s maiden name or full credit card numbers . 

The only exception to the above I have noticed is if you order something from the Apple Store (apple.com), your receipt will be addressed to Dear Apple Customer. That is a receipt for a purchase you initiated.