I really don't understand why can't we just pay a fixed rate of tax, all of us. 20% everyone regardless of your salary. Right now I feel the rates are discriminatory in a sense that a guy who spends 5 more years studying will pay more than a guy who just has a Nkandla High School Grade 3.
Replying to the OP, just quit working or simple earn less as some of the forumites have advised
When paying marginal rates, this is referred to as progressive taxation.
If you want to see a flat tax in SA, look at our VAT.
The problem with flat tax rates is that they hurt the folks on the lower income brackets. 20% of a 10K income will hurt the pocket more than 20% on 20K (this is what is mentioned in justifying progressive taxation)
Also, AFAIK, income tax makes up around 30% of gov revenue, so they won't be adjusting the tax system any time within the next 100 years (unless it is to increase it).