charged for an item i dont even have

on the 27/02 i purchased three items from exact somerset mall . the 28/02 i returned two of the items to blue route mall exact . the one item which was a pink stripe shirt dress was a return and that was processed and credited back to my account . the second item was a black jumpsuit which i bought in a size 10 but i took it back to have it changed for a size 12. on the jumpsuit purchase slip there was also a pair of earrings and a voucher loaded onto the sale for R50 ,so i received R50 off the total . the jumpsuit original price was R299.99 and the earrings was R29.99 with my R50 off the total on my slip came to R279.98. when the size exchange was done for the jumpsuit the cashier Zukin did the exchange on the original price of R299.99. The girl in store who did the authorization advised him it was incorrect and it should have been done on the discounted amount which on the till slip was R254.53. they cashier and the lady assisting him did what they had to and i left the store with my size 12 jumpsuit . the following day i checked my slip and the amounts on there did not make sense . before i "exchanged" my jumpsuit my available credit was R2436.00 , but after i did the return and exchange my credit went down to R2252.00. i need to know what happened because according Kauthar who works at blue route mall exact , Zuki did nothing wrong and customer service also cannot pick up what happened . on my mini statement it shows that three items were returned which was R299.99 , R254.53 and R279.99. yet it shows a purchase for R279.98 . what ever i bought i returned except for the earrings so if anything should be showing as a sale it should only be for the earrings and nothing else . i will not pay this account until someone can answer me about what is going on