DNS translates names into numbers, if you type in : Google.com your device uses DNS to know where to find Google.com
There are some ISP DNS servers that are returning incorrect answers for commercial banks.
The co.za DNS Zone does not yet have DNSSEC and nobody knows when this will happen. The only semi safe workaround for IT Companies is to update their clients DNS Server Settings to use the public Google DNS Servers
Configure your network settings to use the IP addresses 18.104.22.168 and 22.214.171.124 as your DNS servers.