I think EU regulations require that cancellation must be accessible in the same way as the subscription. So online subscriptions must have an online cancellation.
Said button is no doubt “in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying ‘Beware of the Leopard.‘“ because we are all Arthur Dent in this Internet.
https://www.goodreads.com/quotes/40705-but-the-plans-were-on...
https://www.lemonde.fr/en/faq/?question=i-want-to-cancel-my-...