SARS is failing people

My grandmother aged 80 was working as a nurse in a local township in Phalaborwa, she went on pension in the year 2002 October 25th. 2020 she started getting letters from SARS saying she is owing (After 18 years). There is no branch in Phalaborwa & she has aged in a way that she cannot travel to Giyani. She has no knowledge of why she is owing because she just received a payslip by hand & noticed that she pays tax, that's all. Now she is confused how come they didn't deduct the monies when she was going on pension.