It sounds like you may have a website subscription with BetterMe. The website is often a referral from a Social Media post or website advertisement where they offer a Free Trial directly to you on the site that does not involve Apple at all. They do have an app, but Apple can only manage subscriptions made within the app using an in-app purchase. Review the information that BetterMe provides for their Website Subscriptions if that is what you ended up with.
https://betterme.world/en/subscription-terms
Unfortunately Apple is required to allow third parties to manage their own subscriptions even using an app. They have been sued and lost in court where they were required to pay huge fines for previously not allowing it. Later, when they attempted to warn users that their purchase was not being managed by Apple they were sued again and required to remove the warning.
That leaves you with resolving the issue with the merchant, disputing the charge with the payment method being billed, and/or reporting fraudulent activity with a Government agency responsible for reporting fraud.
https://reportfraud.ftc.gov/