The problem is enforcement. Sorry, technological solutions are not workable - there's always going to be a way to get through because there's nearly no risk of enforcement, which is where the work should concentrate. The thing is that the only reason why robocalls work is because there's a nexus before the phantom callers and real businesses buying those services and those businesses have records because they are paying money. So start chasing those records using existing playbook:

Hire law firms that specialize in collecting fines. They will go through reams of paperwork and paper trails and eventually have a sheriff show up at a Thanksgiving dinner of a whoever owns the companies, after their corporate shields will be pierced, taking away chairs, pans, fridge and a turkey fryer.

When that starts happening robocalls will very quickly.