Unchanged Banking Details

I requested change of bank details in October 2014 via Westgate cell c. I realized 3 months later that it was not done. I phoned the call centre and they confirmed it was done. 2 months later I was still in arrears, I phoned the call centre to inquire and the lady I spoke to was very unfriendly. The money owed was paid, and I was made to believe that all was fine. In May 2015 I realized my account was still not debited, when I check my bank statement cell c was debiting my account on d 21st instead of the 23rd as agreed. They keep on debiting 2 days earlier than my pay day, which is not fair. My bank record has been damaged due to un-honoured debits. Cell c is charging for arrears caused by their negligence, which is unfair. I'm also due for an upgrade, but I won't be allowed to upgrade due to cell c's ignorance. The customer care does not respond to any of my emails and the service from the call centre agent's is just horrible. I requested bank details to be changed in October 2014, and to date 28 July 2015 it has not been resolved.