Worst service ever

I have never been this frustrated in my life. I have a WiFi simcard contract with cell c and my initial debit order date was the 27 of the month. But since changing work I went to change it for the 1st of the month since I get paid straight at the last day of the month. I did the changes in February for March payment. But still they are debiting on the 27 and by that time there is no money in my account and the debit order bounces then at the end of the month I have to pay double the amount I owe as there are penalty fees every month since March. I have gone to all the stores even emailed the call center with the screen shots of when the debit order comes of on the 27 but they keep saying their systems shows that my debit order is on the 1st but every month when I get my statements it indicates 27. Now my account is in arrears. This platform is my last resort because now this is going to mess up with my credit score. Worst and bad service I have ever encounter.