DENIED A RETURN - Consumer Complaint for PEP STORES

I bought a school trouser that was a smaller size for my son just before lockdown and it the shop was closed so i couldn't exchange it and i lost the receipt but the tag on the trouser it still there...got assisted by Mamsie who asked me how do i think she must assist me without a receipt i said i dont know and she told theres nothing she can do. i just want to know is it impossible to do an exchange without a receipt or she was just being rude