Bershka Store Won't Replace the Coat I Purchased on an Online Marketplace

I ordered a day coat from Bershka on November 24, 2023, and I obtained this order through Trendyol online shopping site. When my order arrived, I felt that it was too big in size and I wanted to change it. When I connected to Trendyol customer service, they said that they did not make exchanges and that I should contact the seller store. Later, when I called Bershka, customer services stated that they only exchange the products received from the store and do not exchange the products they sell on the online platform. I am currently victimized as a customer, I do not want to return a product I bought at a discount and buy a different size by putting money on it just because I bought it online. If I knew they had such a system, I would definitely not shop. I am sure that many customers like me are victimized, and I demand that they provide a solution as soon as possible.