Анонім

I've recieved numerous calls from this number and every occasion I've managed to somehow miss the call but I've tried calling back every time and get the same message "Optus wishes to advise that the number you have dialed has been disconnected"... Now that's strange as they just called me and I also got the same message the day before so my question is "are they reconnecting to make a call then disconnect?" Doesnt add up. Bit shady