Complain

I have made contact with MTN via the 135 number, none of the consultants are able to give answers everytime I get different explanations, can MTN train people to understand their systems an be able to interpret invoices, I have a contract that I pay monthly that I have not defaulted suddenly my account is behind, I was told that I need to send again the proof of payment which I did one other consultant advised that they have issues with allocation of funds, if that is the case what's that got to do with me as I have paid, why should I get incorrect invoices and adviced that I should pay double,