blacklisted even when the account it's paid up

<p>I submitted a claim for insurance to pay my account as I was retrenched..my insurance made the payment to cellc service provider. . I personally called cellc to cancel my account and the agent I spoke to assured me that it has been cancelled and there is no other payments that will be required as I haven't been using the phone. .. After 2 months of cancelling my acc I got a bill of R1114 which I didn't understand it .. I made few serveral phone calls to cellc however I never got helped. . Right to my suprice I find out that cellc has blacklisted me.. I want a proper answer to why I have been blacklisted </p>