RCS pathetic charges & billing interest to a 6month interest free account!

I've been a Jet/Edgars client for many years, 2018 I paid up and closed the account. I was then called by Jet/Edgars and offered a 6 month interest free account. I took up the offer and remained a loyal client. RCS took over in 2020 I think. I used the account and paid my account as I should. April 2021 is the last statement I received that was correct. Thereafter interest was being added, which I enquired about via email but to date it's gone unanswered. June - to date all statement reflects interest and fees even though I over paid my account each month. Again, I sent numerous emails, I'd get a reply completely unrelated to what was in my initial email sent to them! ***** then occurred on ,y account, investigation took place and the matter was resolved, yet I was incorrectly billed for a card replacement R240 (fees) even though I was informed by the consultant there will be NO charges. YES R240 for a card replacement, which wasn't even my fault how ridiculous! How can they just decide to bill interest, Is it even legal to do this? I've requested reversals of this interest and updated statements not reflecting these absurd charges, BUT NO RESPONSE.