POOR SERVICES MTN

I have received an email from MTN on the 14 December stating I was overcharged and will receive a full refund by the 27 December. I did not receive any refund I am calling customer care numerous times over 25 minutes I have to hold on. I recieved my statement with the correct amount but am being debited extra. Every month I cannot be overcharging and then wait for refunds. POOR SERVICES from MTN.