Can SARS deduct tax that I owe from my retirement fund?

SARS does inform you. It sends out an annual assessment, either by mail, or electronically (if you use SARS e-filing). Of course, this does require you to submit a tax return, and to follow up on your assessment. SARS does not use your retirement fund lump sum to deduct tax that you owe in respect of income - this is not permitted by the Pension Funds Act. But SARS does require you to submit outstanding returns and pay amounts that are long overdue before issuing your tax clearance certificate.