Bad Service

I bought two t-shirts at Identity Eastgate on the 11 of December, I paid with a voucher and put the rest on my account. One of the t-shirts couldn't fit and on the 15 I went back to the same store to exchange but to my surprise I couldn't do that. The price of the t-shirt was R199 & with the voucher I paid R133.37. The till operator refunded me the R133. 37 and then charged me full price which is R199. I asked how come I had to pay full price for the same t-shirt because I'm just exchanging the size? The till operator called for authorization and the first lady came and I asked me if my voucher hadn't expired, I said I don't know and she said maybe this is because the voucher has expired. I told till operator to sell me back the t-shirt that I wanted to exchange because it didn't make any sense to me to pay R199 for the same t-shirt that I paid R133.37 for. He called for authorization, another lady came and the till operator asked him how she was going to make the t-shirt R133 and she said to him we'll just do a price override. I asked how come you're able to do a price override to sell me back the t-shirt that I wanted to return but you're refusing to price override the new size? She said to me she's doesn't want to fail the audit and I don't understand how audit has anything to do with this, how is it my concern as a customer? She even said to me if she overrides the price of this new size, it will be like she's doing me a favor or she's my friend and I said to her I wouldn't mind leaving my original slip with them so that they can attach it to the new slip for the auditors to see why they had to do a price override for me but she refused. It still doesn't make sense to me that she could price override the old t-shirt that I wanted to bring back and sell it back to me but she can't do a price override on the size that I wanted to take. This clearly shows that Identity doesn't care about customer satisfaction but rather they worry about their so called audit that I don't even know how it concerns me