Neglected to close account

About two month ago I closed my account at FNB Kathu branch. Two months later I receive a call from FNB call center demanding payment fro an overdrawn account. On further inquiry I comes to light that the account was never closed and it was bank fees that accrued to over R800. I spoke to people at FNB branch and they are not willing to assist until I confirm who the person was that was supposed to close the account problem is I only saw this person once in my life two months ago and less than 10 minutes, how the heck should I remember who she is. Questions1: How is it even possible to go in an overdraft if you never had an overdraft facility on you \closed"account? Please reverse the so called charge as I am not willing or able pay as I am currently under debt review. I am sure this simply a mistake by the person that helped when I closed the account"