Poor Customer Service

I am extremely frustrated with trying to query an amount on my vodacom account. I have been trying for a month to get hold of vodacom to assist, through accounts, customer care, going in to the store, the constant referral to the chat bot, online agents, everything and I have had no success. I was billed for an amount, after my contract had been canceled, on a number that has now been in use for almost a year, that is associated with the canceled contract. I eventually got through to accounts today, using this number as a reference (because nothing can be picked up on my actual number) and they advised the amount is there, but they cannot tell me what it is for. I was then advised it's for an airtime advance (???) On that number, requested after the number had already been switched to prepaid. I explained I have no transactions on that number, I don't even have access to it, and then she changes to say that the amount is due to the early cancellation of my contract, as part of the settlement fee. I again explain, that I have paid the settlement fee in full and recieved a statement of zero balance AND this amount was only billed 1 month after all numbers had already been converted to prepaid. The amount was never previously mentioned or included in the invoice recieved for the settlement. I am then advised to hold because customer care needs to look into it. I hold for 15 minutes, and am then told customer care needs to call me back, they have system issues - and of course, they have not called me back. I am so FRUSTRATED because I have now been flagged to have an arrears amount, which is reflecting on my bank account as well. I have never before missed a payment, I followed all of their instructions and no one can help me.