My Cellphone Contract Seems To Be Delayed

I have been trying to cancel my cellphone contract with MTN and it seems like they are dragging the process. I have paid off the amount on the 25th of August and made a call today to cancel the cellphone contract. The service provider who's name is Mpho told me that I was supposed to make a call within 7 days after making a deposit. Then he said so to me i need to pay more because of the delay I made, and I understood. I then asked him how much is left for me to pay it off, he then said he'll check for me. It took him more than 7 minutes and after that he hung up on me without getting back to me. I have spent 25 minutes 50 seconds in and i am not satisfied with the results i got.