Edgars are Rouges

Edgars are ripping people off: My instalments at edgars is about R250, I made a payment off R1000 on the 6th of September 2015, the receipt from the store showed my balance is R4629,84, I only purchased for R398 in September, I made another payment off R1000 on the 3rd off October 2015, my receipt shows my balance is R4458.40. Just to let you know my instalments is now R200. When I queried it with customer service, they said its because off the interest and that's not my balance on her system shows R4800 . I just don't understand how this is possible, the receipt that I got from the store and the amount from customer care don't add up. the only additional thing on my account is R39.50 for edgars club member and R40 for cell phone insurance. How many other people are they doing this to.