Bad service experienced

Bought bra's @ Jet store in Mall of the South on Monday 02/09/2024 my size and the cup size is what I normally buy unfortunately when I got home the cup feels small its suppose to be DD not sure if is the design or something wrong with it ,today 06/09/2024 went to exchange to my surprise they refused telling me stories about underwear policy though I never wear the bra's I felt it is so unfair to me my question is whats the difference if tried them in store or home, So my money is going down the drain