Customer complain

I bought a lunch container with a bamboo lid. After washing it ,it changed the shape. I returned it and the assistant lady argued with me that I've placed the lid in the microwave even after I told her multiple times that I didn't. She is the rudest assistant I've ever encountered with.(Mapule) She has attitude for days. What kind of training do they get to think they can give us that attitude and even argue with us about a quality issue?and this is not the first time I've encountered such a problem with sheet street at the grove. It seems like they do as they please with customers. The manager didn't even reprimand her when she was rude.They telling me that because the lid is bamboo I'm not suppose to wash it with hot water that's why it lost shape, that i know but i washed it with warm water, and if I were to argue that container didnt even have instructions. I just wanted an exchange and a whole manager tells me she doesn't have authorization . Like really? The manager can't assist me because she has a stock take the following day, how is that my problem?