Unfair Billing and Bad customer service

I had a Telkom contract account which I paid properly but then I had financial difficulties and could not meet the payments which made my account to be handed over to the collections department, I recently app**** for debt consolidation of which allowed me to be able to settle my Telkom account. I received an sms confirming the balance to be paid to settle my a account was R1306.00 I paid an amount of R1310 on the 30/11/2018 to settle it . Today I called their customer care and spoke to KAMO to request a paid up letter and I was advised that I still owe a balance as I was billed for the month of Dec however the lady told me my services were suspended in August 2018 which I didn't understand why I was billed on a suspended account of which I was unable to use the data they were billing me on, she then advised that she will not even escalate the mater for me because that's how the system works and it was not going to help for her to escalate the matter for me. All I want is a paid up letter for the amount I was given to settle and I must not be held liable for the extra billing that was charged on my account since the account was long suspend and they must reverse the December billing and bring the account up to date