MTN Keeps billing

I went to mtn to cancel my internet contract in November. The guy said I has been cancelled, now i get a invoice for R1270 because apparently I couldn't cancel because I still owed R200 which was never told to me. MTN refuses to cancel the contract and says they will keep billing me event though I have not once used the data after I cancelled it.<br> <br> Why should I pay if the person who cancelled my contract did not do his job.<br>