When I try to unsubscribe, I’m told I'm not subscribed!
If you try to unsubscribe and get an email back that says, in effect, “You're not on this list,” yet you're receiving posts, please trust us, you aren't on the list! However, a different email address of yours probably is and it likely forwards mail to the account that appears from your perspective to be subscribed.
In this situation, the only thing that can be done is that you unsubscribe the address that is subscribed. Unfortunately, we usually can't tell you which address that is, so you'll have to go back through the addresses you've had in the past to narrow down the list of candidates.