Somehow I managed to end up with an account with Greasy Palm (www.greasypalm.co.uk) and I get a lot of mailings from them.
Fortunately, they go to a webmail account that I use as a sacrificial lamb.

I just clicked the unsubscribe link, which contains the username and password, and it said they were invalid. I requested my username and password by email and it sent me the exact same ones, which of course, failed.
They also fail to log me in to their website.
It says if you have any problems, contact support, so I clicked the link for support. The FAQ said nothing about unsubscribing or login problems, so it suggested submitting a ticket.
I clicked the Submit a Ticket link and it said "You must be logged in to submit a ticket".

I re-read the Ts & Cs and it says that if your account is dormant for over 12 months, it will be closed. I'd say mine was definitely well over that limit, which is probably why the login doesn't work. However, they keep sending mails to my email address.
I guess, technically it is spam, so they're in a very dodgy position.