Nothing wrong with the module. You have not set up a Zone for South Africa and/or not checking out with a South Africa billing address.
Admin>Locations & Taxes>Tax Zones - click New Zone - input a Zone Name and Description (input whatever you want e.g. S. Africa) - click Save - click on that new zone that has now been created - click Insert - select South Africa from the Country drop down menu, leave All Zones selected in Zones - click Save.
Now back to Admin>Modules>Payment - click Bank Transfer - click Edit - select the Zone Name that was created (e.g. S. Africa) in the Payment Zone drop down menu - click Save.
The module works as expected when checking out with a South Africa billing address.
