I have worked and paid tax as I earned until September 2011, since then I have earned an income, how

You would include this income under the section "foreign service income" If the amount was paid from a foreign company in a currency other than Rands, you would need to convert this to Rands using the average exchange rate for the period which is published by SARS. When you include this in your tax return and then file, SARS will determine the tax payable.

Basically your income will be added to your PAYE earning income to determine your overall income which is then used to calculate your taxable income.