Billing problem they will not admit fault

they took away my data bundle then reinstated it after one month and charged me out of bundle rates and will not refund me, when i ask to speak to a manager at the call center they cut me off, i have been to the Menlyn store and they have admitted fault but say head office accounts refuses to budge. the manager at Menlyn Sue has really tried to help logging many calls and cases on there system for me but even she says she does not Know what to do anymore. i sent a mail and the reply i got was \we will reply in seven working days"i have been waiting 21 days already for this to be resolved and no joy. i was a Nashua customer and have had nothing but issues since Altech have taken over"