Cell C Attorney *****

I cancelled my Cell C contract in July already this year but it was scheduled for end September which I was fine with. Cell C then sent me a contract cancelled notification at end September however I got a call from their attorneys Shaiks Shapiro saying I owe them money. Is this retribution for cancelling my contract. I don't owe Cell C anything. Why do you treat your customers like '****'. I have tried to call Cell C and the call centre says there is nothing owing on my account so what is going on. Cell C please explain!!! I have been a customer for years and just because I cancelled a contract is no reason for this treatment.