If you are on a do-not-call list and getting solicited, you can contact your state attorney and turn the caller in. Worked here and the company, (which the state had been trying to get shut down somehow) was fined over $150k.
As for the unsolicited credit card aps, the best thing that seemed to work for me was to write in big magic marker across the application: STOP SENDING ME THIS SHIT, place it in their envelope with everything they sent. They will stop. Citibank was sending us two apps a WEEK-we don't get any now from them. Now on to Discover cards....
The only time sending change worked was for an outstanding hospital bill that I was getting harrassed for-it was for $.37. I sent 3 dimes. The 7c was written off apparently, as I never heard from them again.