When we get junk mail, I gather up all the sweet wrappers, choc wrappers, empty crisp packets etc I can find in the house and pop them in the envelope with their mail and a note saying, 'thanks for the rubbish - now you can have some of ours' ! and just put it back in the post with a label saying 'not known at this address please return to sender'

Ive even received an apology in the past !