Worst customer service company!

I cannot believe the incompetence of Cell C! This is the second report I am writing about them for the same issue! after settling my contract and cancelling it they went and Debited R7331.63 OFF MY ACCOUNT WITHOUT MY AUTHORITY! I was assured that this wouldnt happen again and that the problem will recified but AGAIN TODAY I JUST RECIEVED NOTIFICATION FROM MY BANK THAT I NEED TO PROVIDE FUNDS FOR CELL C TO DEBIT R7331.63!!! MY GOD!!!! I am livid! do these *****s know the inconvience they are causing me!? Do they know the implications of a returned debit order on my credit score!?? Do they know the effects that this will have on my credit profile!? If I could I would make sure that NOBODY EVER USES CELL C AGAIN!!! They are a nightmare!!! Can somebody make sure that this debit order does not run from my account today!!!?? I DO NOT OWE CELL C!!!!