Apex domains cannot have CNAME records.
Question and response
Question
dig adsl.co.za. NS
Answer
adsl.co.za. 5 NS ns4.zonomi.com.
adsl.co.za. 5 NS ns3.zonomi.com.
adsl.co.za. 5 NS ns1.zonomi.com.
adsl.co.za. 5 NS ns2.zonomi.com.
Authority
The response has no authority records.
Additional
ns1.zonomi.com. 3 A 45.79.211.52
ns2.zonomi.com. 3 A 139.162.211.108
ns3.zonomi.com. 3 A 128.199.213.165
ns4.zonomi.com. 3 A 45.79.211.52
ns1.zonomi.com. 3 AAAA 2600:3c02:0:0:f03c:91ff:fe26:5def
ns2.zonomi.com. 3 AAAA 2a01:7e00:0:0:f03c:91ff:fe26:5d77
ns3.zonomi.com. 3 AAAA 2400:6180:0:d0:0:0:52d:3001
ns4.zonomi.com. 3 AAAA 2600:3c02:0:0:f03c:91ff:fe26:5def
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0