trucaller...
I have used it on Symbian and now Android and it seems to work "OK".
What really helps is everytime I get a "missed call" , "hangup" or unknown number I add it to a special contact "SCAM CALLER". A very popular fellow. But the trucaller app has a "block" button. My tip for everyone, if you get an unsolicited call stay silent. The robocallers are listening for live numbers.
My DSL line has a FAX on it.
P.