Before requesting a refund, you are advised to cancel any subscriptions that you do not wish to continue. How to cancel a subscription from Apple - Apple Support. If the subscription is not listed for your account, then you are not subscribed through that account. If you have multiple accounts (not recommended), then check for each.
The linked Related Article has the complete information on refunds. Request a refund for apps or content that you bought from Apple - Apple Support. If the charges are not listed for your account, then you are not subscribed through that account. If you have multiple accounts (not recommended), then check for each.
If you are the organizer for a Family Sharing group with Purchase Sharing active, then you would be billed for the purchases of any of the group members. Users in the organizer role agreed to that.
If a known someone else is also using your payment method, then ask them as well.
If an unknown someone else is using your payment method, then you should contact your financial institution instead.