very angry customer

so i upgraded with mtn on the 30/10. However the person who dealt with the ugrade failed to update the amount to the new billing. I've been trying to get this sorted for over a week now and had no feedback or answer's from mtn, I even called there call center where i got transferred to 4 different people of which no one could help me. I am extremely unhappy with their service and honestly wish i hadn't signed another 24 month contract with them as their customer service is pathetic. Really need this situation sorted as i refuse to pay another month on the incorrect billing.