Staff taking calls near customers

I bought 3outfits in December 2021 at Rosebank H&M,today I went to H&M MallofAfrica to exchange one outfit coz it doesn't fit me, so I wanted to exchange for another size,we spoke to Lebo,when I told them I lost my slip,they told me they can't change for me,that I have to remember the day I bought the clothes,I told them I bought in December cash,but I don't remember the day,they left me one by one, answering call & laughing,I don't know is it because I'm black or I'm a female,2manager came & listen to me & left.