Pause then what I think was call centre noise in the background. Caller then said "Hello anybody alive there........." Yes there is but if you don't tell me who you are I won't answer. I suspect it's electricity telemarketers they've been bombarding the landline..........

Called didn’t leave a message

Caller: 0401 301 333

Missed this call as I was on another call, and when I rang this number back it says “this mailbox is full” so I’m tipping it is telemarketers.

I made a sound and they hung up

Similar experience i.e. background noise then talking about my electricity provider. Mentioned I was not interested and I would be very interested how he did obtain my number...

Caller: electricity telemarketer

She said she was in Melbourne, but could give the street number, and certainly did not sound Australian

Never leaves voicemail. Decided to call back a min after I received a missed call and very suss as a network announcement says"this mailbox is full"

They called me around noon a few times which I missed. When I called them back it just said mailbox is full, try again later. Must be some sort of scam!