Double pay on tax to SARS?

I'm on contract at a certain company. They say, because I am not a fulltime/permanent employee my tax I pay per month is higher then those that are permanent employed. My Q is though if they subtract from my salary R500 for tax and should actually be R250 if I was permanent employed, will I get the difference of "R250 x (the months worked)" when I do my returns at SARS?

You will get the difference in tax you overpaid back from SARS when you file a return each year if too much was taken off as PAYE.