Telkom's incompetence costs me time and money

I cancelled my Telkom subscription in July 2018. They confirmed that the line had been cancelled and my account was closed and issued me with a case number ********** 4. It seems that they are still billing me and are now attempting to hand me over for non payment of account. In fact they owe me R700 for the deposit I paid for the ADSL. They send me final demands but no contact info to contact someone. They send me sms and I respond but still no response from them. People phone and I tell them that I closed the account in July last year and yet I still get billed and the bill is growing every month. Now my credit record is going to be effected because of their incompetence. Please can someone sort this out asap and confirm to me in writing **********