Incorrectly charged for a final letter of demand

I am continously being charged R176.10 for a final letter of demand which besides never having received this so called letter, my account is in fact in a credit. I have emailed and physically been in to the office in sandton and logged a complaint and was told it would take 6 weeks to be resolved and 3 months later nothing reversed off my account and I am still being charged. I have been fighting this since October 2020.