Telkom Account Cancellation and Blacklist Issue

Terminated services of contract in Feb 2017 giving relevant notice, Telkom carried on billing for 3 months and after numerous calls and emails finally got it sorted by Jan 2018 that I didn't owe any money and account was finalised. Received email from Telkom confirming this and the next step was the Telkom Credit Delisting Department was to contact me to issue with a certificate/letter confirming this. Needless to say again nothing has transpired from Telkom's side and this default is noted on my credit file as Telkom haven't done anything about it. Every call to customer services ends up in sending an email detailing the issue and no response nor action forthcoming from Telkom. Extremely frustrating and its affecting my credit record when it is solely an administrative error from Telkom's side. Customer services will not give out a direct email or contact number for Credit Delisting Department. Do not know what it takes to get Telkom to do what they say there were going to do. HELP