Over charged on data and unable to get refund

Was over charged on data with R10 000 4 months ago and am trying to get a refund for the last 2 months. Each call centre agent promised it will be done in 7 days and 2 months later it is still \Trust me sir I will make sure it is refunded. 6 Call Centre agents later and nothing has been done. This poor at it's best. "