Bad customer service

I went to Mr price west gate 2 months ago to laybye my kids clothes. I've been paying as little as I can because I know I don't afford. Today I went to settle and collect the clothes only to be told that I have to return 1 item for R289 because apparently the cashier Thembi didn't do her job right. She didn't calculate the item. I had to take out the R300 that was meant to buy my son shoes, i had to pay for something that was in the 1st place was not my mistake. No 1 took accountability nor apologized. I'm frustrated and angry at this point. May this be seen and taken into consideration.