DNC doesn't work, but my solution does. I have made my default ring tone "silent" and then set the ringtone for everyone in my contact list to something that relates to them. Thus if the call is legit, I usually know who it is before looking, based on the ring tone. People not in my contact list can still leave a message, but none of these scam calls have left a message so far. I haven't been bothered in six months now.