Cancelled contract paid up by client two months later claim client owes them and took client to debt collectors without any communication to client on what exctaly she owes them on which grounds

Worse experience ever, their lack of not even want to assist, I had a Vodacom contract for a phone so I decided to settle it last year October they gave me the quote and I paid it same day at their Vodacom store, now the following day I send the prove of payment and old the documents as requested for early termination of the contract, after my phone was on prepared, now this early January they submitted my name for debt collection, after two months of contract being settled and cancelled, now they claim I owe them, they have not communicated anything for the past two months before submitting my account, then now I submitted the emailed documents which I submitted to their debt collectors that one they have not explained how I owe them and for what?, they have not claim from me before even submitting my name, the amount I paid them for settlement it’s more that what they say I owe how does it make sense, I submitted prove the debt collectors are not going back to Vodacom with these facts they keep calling me I’m telling the answer it’s still the same I don’t owe them nothing, worse Vodacom don’t have a solution when I ask them they dismiss me and keep referring me to different departments of their company without an explanation of where the amount is coming from, the want to mess up my credit record with no grounds no explanation and no one wants to give me answers because someone did not do their job at their company and no one wants to account , why do you want payment and want to blacklist someone without claiming the amount and you also can not explain on which basis the person owes you and the debt collectors have prove of everything thing was done according to procedure instead of going back to ask the company that handed them mandate they busy harassing the client who actually owes nothing, are supposed to pay for things we don’t pay because big companies say we owe them for no reason and no further investigation while these prove that you made error on your side, as a provider it’s worse because you cannot just jump procedures and expect no one to ask this question.