I called back number (02) 9160 4374 reached voice mail but did not say for what company.

Whst so-called calls at 11.18pm at night and leaves a nonsensical message??

Caller: don't know

They called on this number immediately after a call from (03) 7019 5332 which I inadvertently picked (but no response on their end) - so presumably connected

Three missed calls from this number on 22/04/2019.

Caller: don't know

They are a scam / fraud relating to foreign exchange.

They won't talk to you. The f*ckers just threaten to keep messaging you unless you click on a website which will have malware on it. So that's not going to happen.

1 message per day I assume it is automated.

I have tried ringing the number to have a polite?? discussion. Voice says the number is unrecognised