Metal cup hygiene mishap

I received a metal smoothie cup as a gift on 29th Feb 2020, which i did not like and wanted to take back to the store.

When i arrived i was told "we cannot exchange due to the straw being open for hygiene purposes". Firstly i believe this is incorrect behavior as this was not labelled anywhere on the cup and in any case the straw or the whole cup, should have been sealed if hygiene was such a concern for the store. I am unhappy as this is insulting to us as customers that when we return stuff we are told about hygiene when COTTON ON made no effort on their end. I would like to return this cup and really hope that you will do better in the future.