The country's highest judicial body, the Constitutional Court, refused Hewitt leave to appeal his six-year jail sentence after he was found guilty in March last year by the Pretoria High Court on two counts of rape and one count of sexual assault for incidents with young girls in his charge more than three decades ago.
The victims, all teenagers then, had been unrelenting in their pursuit for justice for what Hewitt had done to them when they were learning tennis from him while he was a world champion.
Director of the organisation Miranda Friedman said Hewitt had done everything he could to avoid punishment, but would now serve out his sentence in a proper prison while his victims could find some closure to their long ordeals.
The girls and their parents were dissuaded from pursuing charges at the time because of the stature of Hewitt, whose name has since been removed from the International Tennis Hall of Fame.
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At the start of his trial three years ago, Hewitt had used claims of mental illness similar to those made by Indian- origin British national Shrien Dewani, who was cleared of charges of orchestrating the murder of his honeymoon bride Anni Dewani in South Africa to avoid facing serious charges in South African courts.
Besides the jail sentence, Hewitt was also ordered to pay 100,000 Rands to the Department of Justice.
The funds will be used by the ministry in its programmes to curb violence against women and children.
Prison authorities said Hewitt would not be receiving any special privileges because of his age, but has been placed in a medium security prison, where he is allowed two visits of 45 minutes per month.