Customer Care - Inefficient System

My contract expired at the start of February so I contacted MTN Customer Care about a month ago to let them know that I will be switching to Prepaid after the expiry. So *****gwa rep**** and let me know that this would be no problem and that I should just let them know when all my airtime is finished so that they can move my number to prepaid. Then I got an invoice a week ago stating that a certain amount will still be deducted from my account and so it happened this morning. I tried to find out what is going on but *****gwa hasn't gotten back to me and it's a week later. When I tried to find out what is going on by calling 808 the system doesn't allow me to speak to the accounts department because my number has already been moved to Prepaid, but the Prepaid department can't help me with queries regarding accounts! How ridiculous is this system and the administrative people at MTN! Thank goodness I moved to Vodacom. At least they have a little common sense. So tired of incompetence and excuses. My Reference number is ***, in case anyone at MTN knows how to use it.