Debiting my Account after it has been settled.

My account was wrongfully debited by Cell C twice, this is giving me a bad credit name. I settled the contract account two months ago and cell c debited my account with the full settlement amount on the 28/07/2015. I am furious as this has caused me to pay bank charges as well as affect my credit name. I called in on the 28/07/2015 and was notified I will be contacted within 24 to 48 hours and up until this day 31/07/2015 cell c has not contacted me. I am very unhappy with cell c's service. This matter will not be dealt with in good way, I can assure cell c that they will have a law suit on their hands because of every single inconvenience they have caused especially with the charges I had to pay and mainly because of the bad credit name that they are causing for me.