between 10 and 20 calls a day

I've got caller-ID, so I don't answer this caller. Nonetheless these calls are a constant irritant, especially when I get home from work and want a refreshing nap. I can turn my ringer off, but sometimes I forget to turn it back on. And that is an unreasonable alternative. I would like to answer this caller and voice my complaint but I most likely will be talking to a machine. As many times as they've called with no answer from my end, one would logically think the calls would stop. After approx. 30 days of constant calls, sometimes 3 or 4 in quick succession, these calls are beyond being tolerable. Can you HELP, please.
  Thank you!