Obviously scam call.
Just google '02 9000 numbers' to see all the numbers (02 9000) they fictitiously call from, knowing that these numbers haven't been allocated to the phone system.
I wonder if someone is just dialling numbers to see if they answer and then onsell these answered numbers (knowing they're live numbers) so scammers can call and more likely get their scam call answered.

If this were true, most people have voice mail which will still register as a known number.

If it is also true that 9000 numbers are not allocated then the Telcos have a lot to answer for

Caller: Unknown caller

(02) 9000 7367
Getting numerous 9000 numbers
leaving I message believe it is a scam
call. Always around 5 - 5.30pm

Rang, Answered, No response, hung up. I was curious where 9000 xxxx number were and found this page.

Didn't ring long enough to answer - likely scammer

Caller: Scammer

Scam call, fake NBN