How to Unsubscribe from Mail!?

 Since signing up for xFinity internet service, I have received several promotional emails daily! I've unsubscribed from everywhere I can find and still receive at least 1/day. The emails either don't have an option to unsubscribe, or if they do, it takes me to the page that shows I've unsubscribed from everything already.

It is not okay to send so much spam and not provide an option to opt out. How do I stop receiving your promotional materials?