Service refused over 17 yrs old written off debt of R650

After 3 months of less than 1kbps (paying for 4kbps) due to a 'wet cable' and then 5 days of no internet at all (no reason provided , just 'we've logged a call') I went to Telkom Hatfield for an Integrated Data Sim as I am desperate as my son has to submit online exams and assignments. Telkom Hatfield however refused to issue the sim due to an amount of R650 due from 1999 !! which I saw was listed as 'written off' on their system. When I asked how this was never communicated to me, I was told Telkom could not get hold of me. ????? I have worked for the same employer for 25 yrs, my cell no. has not changed for 20 years, really?? PLUS two years ago the same Telkom approved a new ADSL line for me and NEVER mentioned the R650 ! What annoyed me most was the way I was treated by the manager who was called - as if I was some fugative who has been hiding from Telkom for 17 years. Not one apology for their incompetence that led me to be there in the first place to get a sim, not for their spectacular failure to trace a very traceable person. Out of sheer desperation I paid the R650 and was again told I cant get the sim for 48 hrs until the payment is updated on their system. I am now studying the National Credit Act as I am fairly sure that denying a service to a PAYING customer over a 17 years old written off debt is somehow against the provisions of the Act.