Cell C

According to Cell C, I do have an outstanding account which I didn't pay! According to me, the account is fully paid and terminated. This was done last year September, via Telephone. Cell C now handed me over for collection, but still, nor the lawyers, nor Cell C can provide me with a account statement. The lawyers only send me the amount due, whilst Cell C refer me to the lawyers, namely NBD. Cell C now refuse to answer any enquiry about this account. Please help!!!!