RCS Ripping customers with over charged interest

RCS I have opened account with Sunglass Hut in November 2017 only to find that RCS is regulating everything , I requested that they make 6 month interest free. I bought 2 pairs of sunglasses and returned the other 1 as they looked fami**** the very same November. 1st January 2018 started paying. money owed was R2700. Around march I requested my balance only to find that it wasn't corresponding. I went to Forest Hill Mall to get clarity only to find out that I have been charged interest. when I disputed that I cant be charged interest as I already paid R2500 to date I was given lots of stories. I requested my statement as maybe it will give clarity as how I was charged in terms of monthly fees and so forth to date I haven't received 1. on the 06th April I went again to check my balance I was told am left with R800 and could agree to such, and consultant at Sunglass couldn't help. I then spoke to Charlpon from RCS and explained my story of not going to pay accumulated interest that I didn't agreed to and he promised to resolve the matter in 24 to 48 hours. I went again to Forest hill Sunglass hut on the 17th April only to find that the balance has actually increased in just a week. now my balance is R900. Now am asking myself , is it how they ripping people off by charging more than 200% interest. could NCR please assist in this matter as am not going to pay interest that I have accumulated ********ly, and closing the account with Sunglass Hut. Sunglass you are going to lose lots of customers based on how RCS is ripping people off.