Most robocalls are illegal in the US. We have a do not call list and everything. I believe is it a name change is currently working its way through to change the name to "seriously, do not call... please list".
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https://www.forthepeople.com/class-action-lawyers/robocallin...]
The problem is that determining the source is difficult and even if you did it is most likely over seas where enforcing the fine is impossible.
I would love to hear a technical solution that has been implemented somewhere that had a significant impact.