I called back number (02) 9080 4022 rang once then gets disconnected automatically.

This number is from a company called Informa who run the national Safety In Action conferences.
Their details are

Informa Australia
Level 18, 347 Kent Street Sydney NSW, 2000
PO Box Q1439, Sydney QVB, NSW 1230
t: (02) 9080 4022

I reckon this number is safe

this is for a safety convention taking place mid-september. even i got a call confirming my attendance.

Calling regarding some safety convention. Yet when I google the number I get:

Shaun Kenyon | Informa Australia
Client Liaison Officer

Level 18, 347 Kent Street Sydney NSW, 2000
PO Box Q1439, Sydney QVB, NSW 1230
T: (02) 9080 4022
E: shaun.kenyon @ informa.com | W: www.informa.com.au

I asked to be put on their do not call list