Telkom don't know what they're doing

I called the Telkom call centre early in March to request continuation/extension of the ADSL contract I had which entitles me to a discount on ADSL line rental. The lady I spoke with advised that the details had been updated on the system and gave reference number ***A. I was told that the discount would reflect on my next bill. Subsequently, I received my next bill only to find no discount reflected. I called the call centre again to enquire and after speaking to accounts and sales, now nobody knows anything about the contract or can tell me anything about the call reference. I've really had it with the pathetic Telkom service. Please advise how I can go about cancelling my service as I cannot take this incompetence any longer.