Wrong billing date

I am really ****ed off with the level of service I'm getting from Nedbank, when I signed my credit card contract at the OR Tambo branch I made it clear that the funds should be deducted on the 20th of every month. I see now there's debit orders on the 1st of every month. I never told anyone to debit my account on that day, my ITC record is getting spoilt for such foolishness. I want this to be rectified and sent to me in writing.