I was charged but didn't make any purchases from Apple

Perhaps to look into details in that billing, to determine its source

may be first. Since sometimes fraud or bait email, not from Apple

could be used by phishing or scammer to get fiscal info from you.

If you see 'apple.com/bill' on your billing statement - Apple Support

//support.apple.com/en-us/HT201382

"..If you checked reportaproblem.apple.com and your emailed receipts

and you're still not sure why you were charged, contact Apple Support."

This, to determine if there was an error, in an actual billing cycle.

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

[Or compare to an a fraud or phishing scam.]

Unknown Charge?

1. App Purchase
   1. Curious about a Charge? --> If you see an 'itunes.com/bill' or an unfamiliar charge on your statement
   2. If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
2. Subscriptions
   1. You may view a subscription to an app --> See or cancel your subscriptions - Apple Support
   2. You can also request a refund for a recent renewal of an in-app subscription purchase 

Avoid accidental purchases

1. If it is your device then, please --> Use Guided Access with iPhone, iPad, and iPod touch - Apple ... before handing over a device to a child.
2. If it is your child's device then in the future, enable the Ask to Buy feature --> Request and make purchases with Ask to Buy - Apple Support

It could be Phishing

• Beware of --> Phishing & Other Suspicious Emails 
• Know how to --> Identify legitimate emails from the App Store or iTunes Store 
• Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams —> Use these tips to avoid scams and learn what to do if you think your Apple ID has been compromised.