Mango Denied Product Exchange on My Birthday

When I went to the Ankara 365 Mall Mango store to exchange a gift I got from the Mango online store for my birthday, it was a disappointing experience. The store manager and staff treated me rudely and harshly when they told me I couldn't exchange items I bought online; I could only change the size. Their actions were really rude and insulting. How is it possible that an item that hasn't been used and that the buyer doesn't like can't be returned or exchanged? I have a strong feeling that this goes against consumer protection laws. I want my complaint about this situation and how the store employees acted to be sent to the right people. Thank you for your support.