NEDBANK charges interest on a ZERO debt balance!!!

I have 3 bonded properties (Rentals) with Nedbank....

I use the credit to purchase additional rental units, so I don't close out my bonds as I access the funds when I buy more property.

These bonds are sometimes (as now) paid UP with a ZERO (actually positive) balance....

WHY DOES NEDBANK CHARGE ME INTEREST on this???

I have asked feedback from nedbank a few times....

Its a R0.02 interest CHARGE monthly on ZERO balance....

R0.24 per year on a ZERO balance??

Please explain this to me???

Its not the R0.02 that bugs me... its the principle!!!!!