UNISA and Student Credit Refund

I have a R600.00 credit on my student account and have written numerous letters to the accounts department asking for a refund. Unisa staff do not answer their phones and do not respond to emails. How am I supposed to obtain my refund from them? When a student has to pay, believe me their staff in the finance department are good at asking for payment, however, when the role is reversed, they have amnesia.