Telkom ruins my credit rating

I had a contract with Telkom and after a struggle eventually cancelled it... I got no cancellation letter. A few months down the line I get money taken off my account TWICE using different account references to the one I used to have. I call them to ask why and ofcourse they're clueless as to why it's happening and tell me I dont have any accounts with them, they can see mine was cancelled. I asked my bank to stop telkom from taking any further money off my account. Fast forward a year later, I try apply for credit for something and get declined. My credit rating is horrible because apparently I owe money to Telkom???? Again I call (we won't even talk about waiting periods for them to answer the phone) and I get told I dont have any accounts. I ask for a letter to confirm this and to confirm that my account was paid up and cancelled and guess what?? I'm still waiting!!!! "Sorry mam, it takes 7 working days to draft a letter". I've called 3 times and it's been MONTHS!!!!!!! Telkom is ridiculous