Good-natured (?) spam

TheSHAD0W writes: "Ever since I once used Panda Software's Activescan antivirus, they've been spamming me with advertising. I finally got fed up with it and followed a link to an unsubscribe page, but when given a confirmation link to follow in a follow-up email, I was told "We are sorry that we are unable to process your request at the moment". An email to their customer service address bounced. What else should I do to stop their spam? Has anyone else had trouble getting an otherwise legitimate company to stop sending repetitive advertising?"