If enough people complained, something might get done, but you have to figure out who to complain to first. Occasionally, someone can interest a TV show into exposing them, but it's really hard to prove something like this. You could complain to a state AG, but unless they get a lot of complaints, it won't go anywhere--they're too small-time for that. I get the impression that they were squeezing the last blood out of the business they strangled and left to rot.
I only know what I did and what the reps said to me and I knew that I didn't have enough proof to go to court with this so I didn't--I'd just end up losing more time & money to it. So I just retell my experience when it comes up again.
I have seen a few other people on HN who got burned by them, though. It's sad, because Speakeasy was a really good ISP back in the day, before it was sold and gutted. The original Speakeasy support reps were awesome. But that's gone now and it makes me sad. I've never seen support like theirs from an ISP before or since. You used to find geeks singing their praises everywhere, too, but I'm sure you've never heard that about Megapath or whoever bought them.
I might try to negotiate by offering to pay off some amount, but they will NOT admit that you've cancelled unless you have some kind of proof... which they will make sure there's no way for you to provide. Because their webform sure as hell won't respond and they definitely won't admit that maybe, given that you were using another ISP the entire time, it could somehow be their fault for forcing you to use a web form that doesn't actually work when you've tried it dozens of times and it magically only does something when you have a rep on the phone.
Like you said, they might as well be a scam company at this point. I felt like they'd turned "customer retention" into some kind of hostage situation. I had to play hardball with the rep before their cancellation form magically worked.
My theory is that there's a manual component to the unsubscribe where they have to confirm it with the customer, but they probably don't try very hard (or at all). I'm sure they'll conveniently blame human or technical errors for any faults, even if they've deliberately set things up to fail.
Be sure you document every call, etc. somehow when dealing with them and get legal help if you need to. My impression was that everyone working there is in on the customer retention scam and all the ways to play hardball and abuse their customers. I seriously wish someone would do an expose on them. Speakeasy was a really awesome ISP back in the day. The people who bought them out were scum, so I'm glad they changed the name in a way.