Apex domains cannot have CNAME records.
Question and response
Question
dig dbit.co.za. NS
Answer
dbit.co.za. 5 NS ns3.yourdomain.co.za.
dbit.co.za. 5 NS ns2.yourdomain.co.za.
dbit.co.za. 5 NS ns1.yourdomain.co.za.
dbit.co.za. 5 NS ns4.yourdomain.co.za.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0