Someone please give Edgars accounts department a calculator and basic math lessons

I have an account at Edgars. My outstanding account balance was R 143.33, I paid R 144.00. Any person with primary school mathematics will tell you that I overpaid with R 0.77. Edgars sends me a statement saying that I owe them R 0.12, next month they add an account fee saying I now owe them R 34.12. When contacting customer services the agent also sees that there is something wrong, and tells me she will phone me back. That was 3 weeks ago. Emailing the customer services got me nowhere as well, they keep telling me I owe them R 34.12. When I asked for a detailed ledger of my account, dead silence. No one can explain how I went from a credit balance on my account to owing them money. Not to nit-pick about R 0.77 but what 3 year old is handling their accounts?