The following article is relevant whether you a registering a new .co.za domain name or pointing an active .co.za domain name to a new set of nameservers. It explains the cause of the common error that comes with updating .co.za domains.
The .co.za domain registry works slightly differently from most other domain systems.
They require that a .co.za domain name be preconfigured on your nameservers, before you attempt to update the domain’s nameservers.
Example: you own an active domain name mandela.co.za and need to point it to the nameservers ns1.web4africa.com and ns2.web4africa.com
You need to create DNS records for mandela.co.za on both nameservers ns1.web4africa.com and ns2.web4africa.com. The records must be identical.
If you are hosting the domain elsewhere, you must create a hosting account with your web host before attempting to point the domain to the nameservers they provided. If you are using a DNS service like xname.org, nameedit.com, dyn.com etc., you need to create your DNS records with them before attempting to point your domain to the nameservers they provided.
If all of this sounds like too much technical mumbo-jumbo for you, please consult your web host, server admin or DNS provider for assistance.