Threat to Blacklist a Customer on a Closed Account

I received a call from VVM on 23 December demanding that I pay for a Cell C account that was handed over regardless of the fact that I closed and paid the account in full. On the first call I received from them they demanded that I pay their legal fees, refused to send me an email with a statement and then confirmed that date they received or bought my debt from Cell C happened to be 4 days prior to Cell C confirming my account cancellation and on the same day I happened to close my account with Cell C. When I refused to pay the legal fees with my reasoning and request to send this back to Cell C they told me that my information with the credit bureau would be affected and would not change if I did not pay them. When I mentioned that I would report them to the Debt Collectors Council for refusing to send me a statement of the account as well as her full name the lady thanked me for my time and put the phone down.