Apex domains cannot have CNAME records.
Question and response
Question
dig thumbtribe.co.za. NS
Answer
thumbtribe.co.za. 4 NS ns3.ns3gamco.com.
thumbtribe.co.za. 4 NS vinnig.gam.co.za.
thumbtribe.co.za. 4 NS zippy.gam.co.za.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0