Another way to forcefully cancel a subscription is simply registering with a card to which you can manually add or recharge credit, the day that you do not put money in it (or remove from it), the subscription should be automatically cancelled as they can't debit that amount from you (yeah, it doesn't work if you're subscribed to several services. Or maybe it could if you meticulously add/remove credit the exact days that they charge you provided different days for each service, but that's just too much overhead).
If I recall correctly for example with Revolut it is even possible to generate virtual cards, which is great for security reasons as well.
For people that run their own mail servers no need to use any useful or real email addresses when signing up, simply use netflix@yourdomain.com, amazon@yourdomain.com, etc. Again you have 100% control over those email addresses and make sure that all trash/spam/undesired mail goes exactly where is supposed to go.