CONTINUOUS INCORRECT BILLING

I renewed my contract with MTN in September 2015. Since then, I have been billed incorrectly every month. When calling the call centre, they cannot assist me as the renewal was done telephonically. Does this mean the sales consultant can load any amount they want and the customer just has to pay?<br> I have e-mailed both the MTN customer care department and the sales person who upgraded my contract on numerous occasions. All I receive is an automated reply that somebody will be in contact with me.<br> I am posting this so that somebody can assist me! Please stop taking money that does not belong to you and bill me correctly!!!!!!