What is the exact description of the charge?
Apple only has control of subscriptions that are purchased in the app. Those are easily cancelled here:
View or cancel app subscriptions on iPhone - Apple Support
As with any other purchase/subscription that is not managed by Apple the solution is the same. You must first contact the merchant and it may require more than just checking on their website. You may need to talk to them directly in case you have a subscription using a different email address/login that you checked on their website. If you are unable to resolve the issue with the merchant, then you must dispute the charge with the payment method that is being charged.