As u said in this post 'people are just people, they make mistakes', well you did a mistake too. It`s true that you shouldn't be able to buy a cloth once you have it but you could avoid that by paying just a bit of attention... I would be surprised if they give you the fragments you bought since there is not system that allows you to have extra fragments of clothing as you could see.

P.S. Just my opinion, i`m not attacking/defending anyone. I hope you`ll get your currency back and next time you want to buy something just double check if you have it already so that won`t happen again ;)