Pests, vermin, scum, simpletons and the intellectually challenged have somehow learned to talk - they don't know their numbers therefore don't know how to dial --- so a robo-dialer accommodates.

If I'm bored, I'll punch the number and wait to hear "Your call is next."  Then I say a few obscene phrases quickly but in Sicilian.

Best advice is to ignore and

Received a call from this number. No message left and after reading other comments, I have blocked this number as it sounds like a scam/telemarketing call.