I receive unwanted commercial phone calls around two or three times a week, where they want to sell me things, which of course I never want.
I live in Belgium. We have a law that forbids commercial calls if your number is explicitly registered on a list, which I have done. However with the globalization, some companies now use foreign call centers to circumvent the law and still call you, explaining the two to three calls I still receive each week.
These call centers are relentless, and they're often the same people working for various customers. I know that because the voices that call me are mostly the same (not similar: the same). The number is hidden so I can't get it. Also, my provider can't stop them because even if the number is hidden (and they have to respect that), they use a different number every time from various countries, I'm told. Being professional, I can't not answer a hidden call.
I tried everything in my book: politely declining, playing along to grab the name of the seller in order to ask them to stop doing such practice (spoiler: they don't), abruptly end the phone call, playing bagpipes on the phone, being very rude, reversing the situation where in the end I try to sell them something, etc.
Nothing works: in the end the very same group of three people will call me for different customers.
How can I force/trick them into not calling me anymore?