Return denied, bad client service

I bought a swimming costume. Two days later I returned it because it was not fitting, I was told I can not return that because the hygiene plastic is off. I told them that it was an item on sale I bought it like that, there was no hygiene plastic on. Then I was told anyway the costume is categorised as underwear . I returned a costume before to Edgars that is why I did not fit it in store. I was not told when making a payment that I will not be able to return the item. How was I supposed to know as a client that a costume is categorised as underwear

I was assisted by two personnel's who were very unhelpful Nomvula and Tritue from Edgars Centurion.

I would like to know as a client...how do I know if something is categorised as underwear, should we not be informed as clients that "please ensure you fitted this item as you may not return it" What do I do with the item now