When I was called back they pick up phone after 15 minutes later and explain that thanks for your returning call. When asked from where are you calling and they explained We are calling on behalf of Australian Statistic Department Canberra for Survey but couldn't told me what kind of survey? When I was explain I am going to Police complaint about you she was giggling, said in Australia it is legal to do like that? Anyone have any Idea.

called and left a voicemail saying hello and hung up

Similar to all the above. Found this site and released that mobile phones are no longer immune to cold calls from unknown org's.

They keep calling me off different numbers and I keep blocking them.

i just blocked this number after it rang me twice in 1 day. they won't bother me again.....

Missed call from this number. No voicemail message left. Didn't return call.
(assuming it's a Contact Centre from above messages).

I called back number (02) 4038 1416 reached voice mail for a company called Australian Contact Center.

This is Australian Contact Centre, an outsourced sales call centre. Return calls go to a message with instruction to opt out via email. That's one way to get your email address......