wesbank customer care is not helping at all

on the 07th of October I sent an email to wesbank customer care for due date change from the 29th to the 2nd of every month as my business gives me money by then. they came back sameday and asked for my id number I did send it to them. but yesterday when I wanted a confirmation if it was moved to the 2nd today the send me a massage to say they cannot see my original email, in other words I did not send anything and I have even send them the original email with their response. because of their failure to change my due date am going to reflect as a bad payer until the 2nd and am going to be charged interest for no reason. I need this to be sorted out as it is not my problem they must learn to do things right the first time. very angry with their useless service.