Comcast / Xfinity review: Removal from postal mailing list

I want to be removed from their postal mailing list, but I cannot find a way to do this. All of their customer support options are only for customers and you can't chat with them unless you provide an account number. I receive junk mail almost every day from these people. If I ever decide to change suppliers, I can just go to their website. I hate junk mail and there should be an easy way to opt out of this, but I cannot find it. It's annoying, causes litter and pollution, and kills trees. It has no value. I would really like to know how many new customers they actually get from junk mailings.