Zero balance dormant account incurring charges

When I originally opened my account I made a purchase and then immediately paid the balance due at the next counter on the same day around 2 years ago. I have never purchased from them again. Edgars are charging me interest and account protection fees on a R0 balance! I have tried to engage with them however, I am met with an obstinate clerk who insists that their terms give them the right to charge interest, protection fees, and service fees regardless of whether the account is paid off or not. i have also asked for my account to be closed so additional charges will not be incurred on an account which has been dormant for over 2 years.