I have a charge in my card about $13, but it isn't any of my subcriptions

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. Apple has a support article about charges — 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

or go to Subscriptions and Billing - Official Apple Support