Incomprehensible sub-continent female voice. Just hang up.
Providers of landline telephone services in Australia ought to be required by law to provide for customers a blocking facility for these calls. Once you nominate the number to be blocked it should be done.
On the smartphone I can do it, but not the landline.

Spam

SCAMMER! Rang me and claimed to be '"from the government", then started asking if I'd claimed my "free..." (whatever it was, light bulbs or something). I asked him to repeat where he was from, then gave him a loud "F--- off scammer! and hung up. Normally I don't answer calls from unknown numbers, but was expecting a call. And because of that I sadly couldn't give my typical lengthy anti-scammer spiel about how he'd burn in hell in the afterlife, or on a hellish planet depending on his religious belief, for thieving, so he should quit his job immediately and find a new one that isn't based on robbing and cheating innocent people.

Did not recognize number, did not answer, no message left. Rang back got engaged signal. From other comments , blocked.

Five calls from this number in a few days. They don't speak when they call the first time and then call repeatedly although no one ever answers (because the number's blocked, morons!).
Please do not ever answer calls from scammers, or call them back, or this plague is never going to stop. Just do not answer.

Obviously more bottom-feeding scammers. They don't bother to speak when they phone but then call again repeatedly like lunatics. I've had two attempted calls only 20 minutes apart. (Fortunately I'd blocked the number by then.)
Please do not answer calls from unknown numbers or this plague of pests will never give up - and will probably succeed in scamming innocent people. Legitimate callers will leave messages.

This number's called me twice in the last couple of days. No one bothers to speak in order to identify themselves/leave a message, so I assume that it's yet another of the plague of scammers.

called twice, sounded Indian, sounded drugged, said name was Bryan or Bryant

These calls from people/things that never speak never stop.

called me many, many times but when I called back they hung up. Really sys

Called but didn’t leave any messages