Mr Xolani Mahlangu

I bought two school shirts and one grey trouser on the 31st of January 2021 at Pep store corner Madiba and Lillian Ngoyi (Pretoria central)and I lost the till slip,However I used my bank card to purchase the items.I went back on the 1st of February 2021 to exchange the items that I had bought and they claimed that they could not help me, since I did not have the till slip,I then asked the cashier by the name of Poppy Mphake to exchange the items for me and she bluntly refused saying that there was no other way she could help me, I then asked her to check their system to check my duplicate slip,but again she refused,so now I'm stucked with the school uniform that is too small for my child,how can I get help for my quiry since I cant buy a new uniform?