Re: 60 calls a person
"We used to get an international call every day about the same time (withno one on the line)"
IME, if you answer before three rings, it stays dead, if you answer after five rings it stays dead. Computer makes the calls at a rate it "thinks" operators are available to take the calls, assuming a certain proportion will go to answerphone (they get dropped) or ring for too long (also get dropped after about 10 rings), but if more people actually answer than operators are available, you get a dead/silent call.
The computer will also take note of the what happened, eg was call answered but no operator available? This must be a good time of day to call again. Was call not answered at all? Try again at a different time of day.
What really needs to happen is the companies using the "lead generators" should be fined too for not doing due diligence and monitoring on the people they contract to make the calls in the first place. Since it's all "computer data" GDPR might come into play.