R0.54 for late payment

I normally buy on credit due to I do not carry cash or an Edgars card with me (get my number at the back) and pay via EFT asap when I get back home. Unfortunately for me, I paid the wrong amount and was later blacklisted because I did not pay R10 rand for a few months and every month R0.54 was added due to a late payment and due to my error I did not read my accounts because it was \paid in full". No where was it taken into consideration that I have this account for 30-40 years and I have never defaulted. Anyhow"