Bad Service

I had two contracts with Cell C both ending towards end of this year however one of my contracts was settled a few months ago with the amount specified to me. I only received a phone call end of June telling me that i owe this account where as the phone has been converted to prepaid, i cannot understand how this was not picked up in time and i am now expected to pay an amount that i was not made aware of.<br> <br> This treatment of service is ruining my trust with Cell C, to a point that i am thinking of cancelling my current number. The only thing i had requested from the 3rd phone call i received regarding this is that they log a case but till now the only thing i am getting are phone calls bombarding me to make payment arrangements but no one is coming back to me as to why this error was not picked up in time.