38 month term loan

I took out a 38 month loan with Capitec Bank in 2018 for R99 000.00. In Jine 2021 I app**** for covid relive for 3 months and after that I had the loan agreement exted as I could not keep up with the monthly payments. Now at the end of January 2022 I went to enquire about the remaining duration just to discover that I still have over 5 months to go which will result in me paying R303 000 at the end of this period. I noticed thay they add the monthy chargrs and interest onto the balance owing every month which pushes the final amount up and then subtract it from there again. I am not a maths guru but from my simple caculations shouldn't the monthly instalments I am payning be dubtracted from the outstsnding balance? For example. My outdtsnding balance is R82 500.00. I pay every month a down payment of R2805. According to my calculatios 82 500.00 - 2806 = 79 666.50. What they do is adding the 2805 to the outstanding balance of 82 500.00 which get you to final outstanding amount of 85 305.00 and then subtracting the monthly instalments. In this way the final amount on my statement increases every month before the monthly payment. When I app**** for the reduction of the monthly instalments of the loan of R99 000.00 I was told that the remaing balance I owe at that time will not change. Now I discovered that the total cost of the loan has jumped up to over R300 thousand. This is exploiting your customesrs to the extreme. Jow can I make a case against this bank.