Cancel an order I didn't make

And "order" for what?

Where are you seeing this order?

If the only evidence of this "order" is an email, make completely sure its actually from Apple. Most unexpected emails from Apple or iTunes are generally scams or phishing attempts.

See 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

Follow the instructions here to review your purchases-->See your purchase history in the App Store or iTunes Store - Apple Support.