Unfortunately I don't think that's true. I'm looking at you, beer52.com! [1]
(And yes, they were doing this long before the UK left the EU, and are still at it today)
Eventually I sent an email to some random customer support email I found complaining and they actually did it.
This is unfortunate because although I can read German, I can’t write or speak it, so figuring out how to write that e-mail would be a headache.
Edit: Thanks to aboalarm.de, which I learned about from this thread, I have learned the correct formula to use:
> Sehr geehrte Damen und Herren,
>
> hiermit kündige ich mein oben genanntes Abonnement Ihrer Zeitschrift fristgerecht zum nächstmöglichen Zeitpunkt.
so if I do ever decide to cancel, this thread has been quite useful.
https://www.verbraucherzentrale.de/wissen/vertraege-reklamat...
It's based on an EU directive, but a recent one so not all countries have it live yet. More details on the EU directive and the German implementation starting next year: https://www.mofo.com/resources/insights/211006-new-two-click...