Have you tried answering and then just saying the name of the list you've enrolled in? Tends to help propagate to the companies that they absolutely should not call the number again. At least here the companies tend to actively self-moderate and cross-reference against the lists, as the law does get enforced. When I worked in cold-calling call centers in the past, I remember they being strict with teaching the "marketers" what to do when people brought up the local list(s).