APAM on the following grounds:
1) Number calls and when not answered does not leave a message
2) We Googled the number and it came up as a probable "spoofed" number
3) When we called the the number back we get a recorded message that said, "The number you dialed is not in service. Please check the number and try again.
4) Our phone network provider (Vodafone) identifies the the number as spam.

So, with those for bits of evidence, we reckon it's spam!

Called me twice no message left. Suspect scam

Caller: Idk

Calling for twice without leaving any msg. Then call again next day, I just msg that number but no reply

Identified by phone as coming from "Kalkine Pty Ltd" but no response when answered.
https://kalkine.com.au/ apparently a stock market insights firm.
Suspect a scam.

Called yesterday in the afternoon - no message left
Called again today in the afternoon - no message left

Blocked

His name was Mark and he was calling in regard to the Victorian Solar Incentive..I hung up..After reading the other comments I have since blocked the number..

Similar reasons as others rang and didn't leave a message, I don't recognise the number and it appears to be a possible nuisance call. Making others aware.

Caller: 0430 100 369 - unknown caller

Received a few calls from this number and no voicemail message was left. After researching this number and as per above comments, I have blocked the caller and deleted the number.
Thanks all for your help :-)

No message left. I often don't bother answering unexpected and unrecognised calls. Then came here and saw it was what they do.

This number rang but did not leave a message. Can only suspect scam

Caller: Selling property “advice”

Blocked