Here in the U.S. we have a National Do Not Call Registry that a person can subscribe to (without cost). While registering hasn't totally eliminated such calls it has greatly reduced them. Additionally, if we do get an unsolicited call we ask the company/caller for their telephone number, which, generally, they will give us. Then we simply state we're going to report them to the Do Not Call Registry, wherein they apologize profusely. But we still report them.
There have been instances where the National D.N.C.R. has pursued lawsuits against such companies.
Lastly, we ignore as many of the calls that still get through and don't answer the phone for, say, 4 or 5 days. This seems to discourage the robo-calls since the robo-call service gets paid, as I understand it, from their client only for completed calls.