Wrong info received and charged to acc A***

A sales person phoned me and advise that he can sell me a product that will only cost me R650.00 per month and that I will no longer have to pay the large amount on my cellphone. I've asked him numerous time if he is sure I will only have to pay from now on R650 he kept on replying yes. Then when I received my account from them I was charged R474.59 + R525.44 for some 10GB on top of my normal telephone account. I phoned them and advise that I do not want an extra account and thaqt the guy told me I will only have the R650 account. They came back to me and say sorry you will have to pay these 2 amounts. I am very unhappy with service and response even after I request them to please listen to the conversation. They just say I agreed to it. I have no knowledge so I was ********** because of my electronic knowledge. I refuse to pay that money!!!! please can MTN sort this out as I do not get any response from the consultants.