Please cancel my contract with you.

I had a contract phone with MTN which I paid in full at the end of July. I paid off and cancelled the contract now month in month out they send me emails that am owing and I must pay. I went to mtn branch midrand and was assisted by a certain lady. But even thos month I have been sent emails that am owing. What's really happen6with you guys I have paid almost a R1000extra. Am ****ed off and wouldn't advice people to make contract with mtn. These guys are ripping us. Jus canceling the contract takes them 5months and in those months I must pay.