Change of debit order date

I have been an FNB client for almost 10 years now the service I'm getting right now it's shocking, I have a revolving loan with them all I want to do is to change the debit order day, I can't believe it's more than a month now they don't know what to do or who needs to do it, I've called the call centre they told me to go to the branch I went to the branch they are clueless on what to do, can they get someone competent to call me or sort it out urgently. Right now I'm so frustrated and its unnecessary it's just a collection date for heaven sake. How can you expect a person to run business with you if you can't do this simple thing