You may have discovered that talking to a human to get off a Capital One mailing list is nigh upon impossible. Here's how to.

Step by step guide on how to get off Capital One's mailing list

1-800-955-7070
say "no number"
wait for the automated voice to gripe again
say "no number"
Press 3
Press 2
(wait a while)
Press 1
(wait a while again)
Press 2
(wait for a connection)
Press 1
(wait for a connection again)
Press 2

And explain to the nice person on the other end that you'd like to be removed from Capital One's mailing list. You'll have to give them your name and address, and you should be removed in a couple of months.