These aren't shady companies either: they are large legit entities in the US.
I've given them the benefit of the doubt a few times, thinking that perhaps a bug failed to write my update to their subscription database, but after a handful of tries with the same outcome, I realized it is not isolated.
Of course I can add an email filter, but that will not take care of the root cause that most likely affects everyone else too, whether it's a deliberate attempt at denying my request to unsubscribe or simply a bug that nobody has a way to report.
What is a proper gentle nudge to say "hey, your unsubscribe system is broken, please fix it"?
There is usually no contact info available to have this kind of "out of band" communication.