Apex domains cannot have CNAME records.
Question and response
Question
dig vocus.com.au. NS
Answer
vocus.com.au. 5 NS ns-799.awsdns-35.net.
vocus.com.au. 5 NS ns-1707.awsdns-21.co.uk.
vocus.com.au. 5 NS ns-471.awsdns-58.com.
vocus.com.au. 5 NS ns-1500.awsdns-59.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0