I don’t know why I was charged

See: If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support

If the only indication of the charges is from an email or text, be aware that it may be a phishing attempt to get you to log in to a site that appears to be Apple and divulge your password or credit card information. See: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

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

How were you informed of the charge?

If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support will help you determine the validity of the charges.