Multiple messages "you missed a call from ... Who did not leave a message"
They do brief calls so you can't hear / answer, hoping you will call back.

Time wasters! Get rid of them!

Caller: Connect Engergy

They called saying I entered a competition, and then wouldn't tell me what the call was about. I asked three times and said they were wasting my time, so they said they call back later. I asked to be taken off their call list and was ignored. I called back to be taken off, and the message said to leave my number after the beep to be taken off their call list, but then, funny story, there was no beep, and the message just played on loop. They called me three times in two days, during work hours.

Junk!

I called back number (02) 9053 9608 rang once then gets disconnected automatically.