Telkom accounts

I canceled telkom when I moved in September 2018. The next month I got an account for October while I canceled it. I phoned them and the person told me pay just this amount. So I went and pay what I own telkom. Now after months, March 2019 telkom send me it's cancelled but I didn't pay every month so now it's R1300 plus I own them. I paid every month. Didn't pay anything after I canceled and gave the last payment. How can you charge me for a month after I cancel it. That's why your department gave me an amount to pay. Because telkom charged me for the month after cancelation.