Bad customer service

I'm having a contract with mtn ***, the cellphone was ****** from me,i then decided to settlish the account and cancel it so I can take another phone, we call customer service with the consultant at MTN Riverside Mall they gave me my balance which waz R3750 which I made the payment immediately after the call, we then did the cancelation for the contract, because I was in need of the phone I took another one of *** which is R699+R299 for insurance, my worrie is that from April there's extra R399 that I'm paying extra, I went to mtn for querie they told me my contract wasn't payed off and they gave me a ref ***, I called again today they told me I must pay again the balance amount of R2700 like how because my account was payed off??? For now since I don't get any help I'm taking this issue further, I'm not happy at all and even with the customer service of that guy who helped (hello Peter will help). Rergards Duduzile ***