nowadays creditors use robo-dialing to flood people's voice mails. and use overseas #'s to get past forwarding. Only chaning a number works. Also complain to ftc, if people don[t complain - govt agencies will do dick. Do not call lists have no power over creditors (you can write 'do not call anymoer' letters to them, but not sure if it ever works).
remember: creditors make most of their $ by 1) threats and 2) making ur life a living hell through annoyances. Esp 3rd party credit agencies that buy the debt and have nothing to lose.
When you send the cease and desist letter to the debt collector, send it via certified mail with return receipt requested. This will provide proof that the letter was sent and received. If the debt collector communicates with you beyond the single instance allowed by law, this evidence will allow you to seek punitive action against the debt collector.