I received an Apple email about an app purchase I didn't make

This is primarily a user-to-user support forum; other Apple users like you. We don't have access to information about charges to your account. See each of the steps in the following instructions. They include information on contacting Apple Support if the other steps don't help: If you see 'apple.com/bill' on your billing statement - Apple Support

If the only indication of the charges is from an email, 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: https://support.apple.com/en-us/HT204759

and https://support.apple.com/en-us/HT201679