Cell C incorrectly handed over my account after receiving payment on time

I cancelled my contract with Cell C on 19/12/2023. Received a bill for the period 19/12/2023 - 19/01/2024 which was settled in full on 8/3/24, before paid date. Hereafter I received another bill for closing the account which was also paid on 2 April 24. My account was handed over to debt collectors who are harassing me even after I have emailed proof of the payments and have explained numerous times. They are now using my ITC details against POPIA legislation and obtain alternative contact numbers as I no longer answer their calls. Cell C is not adhering to section 129 of the National credit Act as my account was never in arrears so why did they hand it over? I went to the Cell-C branch at Loch Logan Waterfront to seek assistance. I was advised that the account was closed and all outstanding money was paid. I also called the service centre who confirmed same but was informed that the agent cant call the debt collectors I must do it myself. Great customer service! I will be escalating the matter to the Financial Ombudsman for assistance.