In the mean time I found how to do that and I’ve cancelled my account.
That process is easy, fast and straightforward. What is not straightforward is that you have to click the link in your invoice that takes you to the page where you can cancel the account. And there is no hint that this is what you have to do to get there.
Incomprehensibly complex and needlessly frustrating.
Thank you for thinking along.
For future reference:
You get a mail message with your monthly invoice. That message contains a link to the order. It takes you to a web page that displays what you paid and when and it also has a button to cancel the subscription [at the time of writing this was valid]. So, it’s super easy to cancel that subscription, but it’s a complete mindfuck how to get there and there’s no easy way to find out that’s what you have to do.