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.
Report it to their email service provider via the abuse@ alias[1]. Tell the ESP what the problem is and ask them to contact their customer and clue them in. Reputable ESPs do this regularly.
[1]: Use the “Received” SMTP headers to see which ESP a message was sent through: https://mxtoolbox.com/EmailHeaders.aspx, https://www.lifewire.com/email-headers-spam-1166360, https://www.smtp2go.com/blog/effectively-report-spam/
It’s great to detect security leaks, but I can also just delete the address and then any email to it will bounce. This usually gets you off their list anyway after a hard bounce.
The only thing you can do is consider it a kind of digital chicken pox. It will always be a part of you, but hopefully it will remain inert. Never do anything to acknowledge that you have seen the messages or that you even remember that the sender exists.
Alternatively, look up folks on Linkedin working at that company, preferably sysadmins/devops/whatever-its-called-this week, and e-mail them?
Same situation. Humans were involved, and it was resolved.
I marked our PM's marketing as SPAM because they're sending emails to me when I never signed up for one.