You can only use our nameservers names (like ns3.m****here.biz/ns4.m****here.biz or ns1.g********.com/ns2.g********.com) for .co.za domain names and not the ones under your name(like ns1.your-service-domain.com/ns2.your-service-domain.com). This is because the registrar matches Nameserver address with the address in rDNS (PTR) record for the nameserver IP.