These are telemarketers who consistently call my house here in Toronto and refuse to cease. Few of these have call display info, so I need to research them on the internet. Still, many have no information. The CRTC should regulate this better, as it is very annoying. The “Do Not Call” law should be upgraded to be more all encompassing.
In the mean time I use my Panasonic phone, which has a ban list, but I still get a single ring. My phone keeps track of all our incoming calls, and I track unknown phone numbers. There is some work involved to keep this list current, but the payoff is that you reduce, to a bare minimum, the number of repeat telemarketers.