Since you did not find the subscription using the provided link, that means it is not managed by Apple and you signed up for the trial on their website. This bypasses Apple's ability to manage or cancel the subscription. You must know how you arrived on that website and it may have been through a Social Media link or website advertisement. Getting the app is not why your subscription was started and you would have been billed for the trial/subscription with or without the app.
In order to cancel the subscription, you will need to do that on the website where it was started. When going to the webpage, next to the button that says "Try Ornament", there is also one that says "Manage Subscription", and that would be the first place to start. There is also more information on cancelling the subscriptions in their Terms of Service. Additional information includes identifying your subscription type and what to do if you don't know the email address used for the subscription.
https://ornament.health/legals/terms-of-use
All the information is there for you about cancelling the subscription and in addition there is information about the Refund Policy they have. More information about their Refund Policy can be found here:
https://ornament.health/legals/wl-refund-policy