When you hit the unsubscribe link in their email you will be taken to their "Service Letter Management" page where you can make changes to your subscriptions including the frequency of the emails.
Tried that. Didn't work. It got to the point I had their "Service Letter Management" page memorized & could probably navigate it blindfolded. The emails just...would...not...stop.
EDIT: Oh...looks like I have a "kill on the server" filter in my email program for their stupid newsletters. Maybe they never stopped and they're *still* coming. Whatever...at least I don't have to lay eyes on one ever again.