Do I owe SARS or do they owe me for the past twenty years that I worked?

It would depend on what your earnings were each year. For 2013 the annual tax threshold is R63,556 income for the year - so if you earned less than this, then SARS doesn't ask you to pay tax. The years previous would have had a similar threshold, except lower for each year because of inflation. So if you earned quite a bit less than this amount each year for the 20 years then you might be safe, but it is a good idea to contact SARS on 0800 00 7277 to find out. Rather be on the right side - the tax compliant side - of the law!