Poor service delivery, incompetence

The worst decision I have ever made was to take up an account with Cellc. I have been calling them since July but till date I haven't had a straight response, what happened is that I had a contact with the I paid all my outstanding (settled the bill) in order for me to be able to cancel my contract, three payments were done, I called in they were able to "cancel" my contract guess what a month later I get an email from them saying that I owe them I called in and I did not get an response what I kept getting were reference numbers with no valid resolution today I got an sms that my account has been handed over, how do you hand over an account whereas a client hasn't gotten any response? This is affecting my credit score so badly I regret taking up a contract with Cellc, nightmare I tell you