.co.za domain

As you can read in the article:

Strangely enough, it seems that you were able to configure the nameservers, but according to your description, the settings have not taken effect.

Judging by this statement:

Which is explained by:

Note that in some cases, this limitation is not placed by the domain provider but by the registry itself. If so, the domain cannot be hosted here, regardless of which registrar you choose to use. It’s possible that .co.za domains have this restriction as well.