First, you scroll down all the way to the bottom of the page where you click "Pocket Premium" in the footer.
This will bring you to the Premium landing page, you click "Get Premium" which takes you further down that page listing Free, Annual, and Monthly paid options. Nothing alludes to you being a subscriber yet, so you need to choose one of the buttons ("Select this option") to be *finally* taken to the https://getpocket.com/premium/settings page (very intuitive, I know) where you can see that yepp, indeed you forgot to cancel your sub.
Credit where credit is due, no dark patterns of "are you sure, you will lose all these benefits!!" bullshit from here onward, one click and your subscription is cancelled, but sheesh, what the actual frock, Mozilla??