Apex domains cannot have CNAME records.
Question and response
Question
dig vocus.network. NS
Answer
vocus.network. 5 NS ns2.vocus.network.
vocus.network. 5 NS ns1.vocus.network.
Authority
The response has no authority records.
Additional
ns1.vocus.network. 5 A 203.134.64.67
ns2.vocus.network. 5 A 203.134.153.66
ns1.vocus.network. 5 AAAA 2403:4800:1:1:0:0:0:1001
ns2.vocus.network. 5 AAAA 2403:4800:2:1:0:0:0:1001
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0