Account query

I have an acc with Nedbank Everyday Current Account with NO overdraft. During March I made a purchase at Lowveld Wholesale of about R664.00 and it was successful as I had enough money from my acc and I also received an sms notification. To my surprise I received an sms beginning July saying I'm owing Nedbank an my account has been handed over to their debt collectors. I then went to my branch at Brown Street in Nelspruit to ask as to how come I'm I owing as I had money available on my account during that transection and no one called me about that before but only got funny sms after 3 months I was told that they can not help me but need to call the debt department, then the consultant called on my behalf but as I heard that what she was saying was incorrect I asked to speak for my self to the debt dept consultant. I then spoke to Linda and explained what happened but she was very rude and unprofessional to me in such a way that she even dropped the phone in my ear...i then called again and spoke to a Zulu speaking lady who then advise me to send an email that she will send to her management for assistance.Since then no one came back to me, but just keep on receiving treatining sms