Poor service from Rosebank College

I registered my sister at Rosebank College in Feb 2020. We paid her school fees in cash and slightly over by R1900. We sent all the relevant documents to the school requesting to be refunded. It has since been a struggle. At first we were told they couldn't refund us due to the pendemic. We are now out of lockdown and they still haven't refunded us. They don't respond to phone calls nor provide a response via email.