school fees rip off

I registered my son at Kingswood this year for Grade RR. i was given the school fees structure for the year which stated that i will need to pay an amount of R1400 every month which i have been doing every month. end of September, the school sent my son's statement with an outstanding balance but 2 payments that i made were not reflecting on the statement. i went to the school to enquire and it turns out that the school owes me R2000 because they apparently gave me the incorrect fee structure for the year. A request was then made that i get a refund and the Director named Pat, said that she will not make the refund as I paid extra money. I do not understand why I am at fault as the school was clearly not organized by sending me the wrong school fees structure for the year. I do not intend on taking my school out of the school but I cannot have the director of the school telling me what to do with money that is rightfully mine.