Cancel contract

I had a data contract with 8ta from 2011. In 2016 I decided to cancel the contract. I visit the Telkom store at Loch Logan Waterfront in Bloemfontein. Cancellation Form completed and I received a reference number. Last day of contract - 31 December 2016. Last of payment - January 2017. February and March they still put the debit order through my account, which at disputed at my bank. After e-mails and new references numbers they cancelled the contract. This month I apply for a contract with MTN. My application was declined - reason I am on the credit bureau. They listed the amount - R400 - as written off, what a joke. I need this to be taken on from my name. I work for a financial institution and I am not allowed to have a bad credit record. Telkom is playing with my life/work.