Vodacom is useless

I am disappointed with Vodacom...I have advised them numerous times to debit me on my pay day 25th of every month, yet they debit my account anytime the please - sometimes it's on the 23rd or 24th or 25th depending on their moods. I have continuously pay additional bank charges cause if this. I cannot wait for my contract to end cause this is ridiculous. Your incompetence is affecting my credit status as I am deemed as unreliable by other creditors.