Bad credit terms and customer support

I opened an account with lewis stores in December 2018 , for about a purchase of 24500 , as per the invoice , after the signing of documents and terms i did agree to a certain extend. When i make a payment of 1500, my account still say balance outstanding of 24200. I went back the next month to pay and released my account is more ,it went to 25600, i was shocked and immediately investigate. They provide you with an contract that stated ,you will pay interest for a certain amount after 3 years as well as account fees and insurance . But they never say that you will pay double interest and insurance fees. My interest on my account alone for a month is between 480-580 , my insurance is 254 and account fee is also there . So you pay other than the premie an another amount of 750 per month apart from your normal debt. The theory of the matter is the interest and insurance calculated on my account contract does not reflect what i am paying currently. 580 x 36= 20880 and 254 x 36 = 9144 , combine that you will get R30024 , THIS IS WITHOUT SERVICE FEE AND EXCLUDE THE PURCHASE TOTAL. My plea to get a settlement discount fell on deaf ears. I went to the store asking the manager if i can get a settlement discount which he said he was not sure its allowed . He promise he will get back to me , but i think after i paid R11000 on my account he wont worry too much , Still this is what you pay for at Lewis .