When you enter into an agreement for services, it’s usually not sufficient to just stop paying. You may still be liable for the charges if you haven’t gone through the cancellation process you agreed to.
As a consumer it's not obvious to me I'm still liable for services after those services have been cut off, which is pretty much always what happens when the renewal fails. I'd imagine services like privacy.com and virtual credit cards wouldn't exist if companies were going after people like me.