Apex domains cannot have CNAME records.
Question and response
Question
dig hostdns.co.za. NS
Answer
hostdns.co.za. 5 NS ns2.clusterdns.co.za.
hostdns.co.za. 5 NS ns3.hostdns.co.za.
hostdns.co.za. 5 NS ns4.clusterdns.org.
hostdns.co.za. 5 NS ns1.clusterdns.co.za.
Authority
The response has no authority records.
Additional
ns1.clusterdns.co.za. 5 A 41.76.111.83
ns2.clusterdns.co.za. 5 A 154.0.166.77
ns3.hostdns.co.za. 5 A 198.244.190.151
ns4.clusterdns.org. 4 A 160.119.253.29
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0