Answered phone call and no one said anything then hang up a few seconds later

This is one of 3 unanswered phone calls on my phone since Sept 28, the other two being 0490 860 627 and 0490 860 495. They are all computer generated calls which do not leave a message if unanswered but connect to the spammer in response a voice. I get calls like this all the time on my landline. When I answer them I usually get Nicole "from NBN" telling me to call an engineer or my internet will be cut off. When I tell her I don't have the Internet on my phone she hangs up. These calls are also from different numbers, mostly interstate.