Apex domains cannot have CNAME records.
Question and response
Question
dig dextrad.co.za. NS
Answer
dextrad.co.za. 5 NS thor.ns.1-grid.com.
dextrad.co.za. 5 NS thor.ns.1-grid.co.za.
dextrad.co.za. 5 NS thor.ns.1-grid.co.uk.
dextrad.co.za. 5 NS thor.ns.1-grid.net.
Authority
The response has no authority records.
Additional
thor.ns.1-grid.co.uk. 2 A 41.61.100.12
thor.ns.1-grid.co.za. 3 A 196.43.195.12
thor.ns.1-grid.com. 2 A 41.61.100.12
thor.ns.1-grid.net. 2 A 196.43.195.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0