Bad service and faults pricing

1st of March i bought 2 x jeans at Identity that marked 50% off one was R250 and the other R290 i bought with my Identity account so when I got home I checked my slip i find that instead of R290 i was charged R575 so I went back to the shop the next day and told the manager that i was charged R575 instead of R290 as it is marked so with big letters, she scan the Jean and said no this one is not discounted is a mistake the only she can do is to credit back to my account i said no this marked R290 can she overide since i just all the from my and only to find is their mistake. She said she doesn't have authorization to overide i asked her to call HO since she doesn't have authority, she can't she will just credit back to my account So i don't understand i get an SMS that Identity have a sale upto 50% then i get there and being invoiced normal price but the item marked big with 50% discount and when i complain they saying they will credit back to my account Identity Riverside mall Nelspruit