I used the prepaid return envelope included in the package to send them a quickly scrawled note about what I think should happen to people who make such offers to me, but the contents of it are not appropriate for posting here.

Many years ago, I read about one guy who got back at some direct mail company in a novel fashion. He taped the prepaid mail postcard to a brick and mailed it. The Post Office delivered it to the direct mail company postage due (at today's rate, that'd be 41 cents per ounce). I don't know if they'll still do that but he reportedly didn't get any more offers from that company.