Contract switch and mixed up bills

I have switched from my finished contract to a top up month to month contract without a mobile device.<br> After the switch I received 2 bills which together wasn't correct. I went in store at Menlyn and asked for the correct amount. I immediately paid the amount as stated. -2 days later I received notification of an arrears account and phoned client services to confirm the amount, again paid it immediately. A week later I received an email threatening to hand the case over to the debt collectors for the first amount (that was already paid). Again, I phoned client services and they confirmed my accounts are in order and paid, I asked them to transfer me to their pre-legal department to confirm that everything is in order. After waiting about 5 to 10 minutes each time for 3 separate calls I got through to a consultant. They confirmed the accounts are in order and that it reflect negatively on my account as I made late payment. Honestly, who is at fault, me or the service provider that messes up the bills.<br> <br> Cell C's after sales service is confused and out of order and paints the client in bad light due to their incompetence to provide quality service. Good prices, bad service.