I think you've derived the wrong point from my stance.
Theft. In my eyes. Is on a sort of sliding scale with regard to ethics.
Stealing from an individual is reprehensible. Stealing from a corporation that nets more than one billion dollars annually? You have a moral imperative to take whatever you can get from them.
I day "Steal" more affectionately with respect to coding. Context matters deeply. Data should be free dah. And the socialism. Good.
I had an idea, personally I just use the Google phone app it seems to do a pretty good job of blocking spam calls somehow. However I had a funny idea. I suspect that these robocallers May be able to recognize the we're sorry your call cannot be completed as dialed tone and words which may signal to them that the number doesn't work.