The problem when unemployed is that you need to monitor your phone for job-related calls, so you have to keep the ringer on.
Also, my particular cell phone makes it really difficult to blacklist numbers.
I seem to recall that the rules state that if you send them a note by snail mail, they are required to stop contacting you by phone.
Recently I was late on paying a Chase card, and I literally got called every single day about the matter. Eventually I called up and said, hey, I'm unemployed, I'm waiting on a check to arrive, and the rep explained that they will be robodialing my phone every single day until it is paid.
For a while I was giving out my skype number instead of my cell so they wouldn't keep harassing me, until I realized that I had enrolled in two step authentication using my phone as the second step. That meant they would always have my cell phone number. Which really sucks.