Stradivarius Shipped The Incorrect Item and Denied My Refund

I recently made a purchase from Stradivarius worth over 13,000 TL but they sent me the incorrect item. When I reported the issue, I was directed to a store to complete the return. At the store, they accepted the incorrect item and explained the situation to customer service, assuring me that there would be no issues with the refund. However, after some time, I received an email stating that they were unable to process the refund. After spending such a substantial amount of money, it is unbelievable that they could make a mistake, waste my time with the return process, and then deny my refund. I will file complaints everywhere because this is unacceptable. The number of the order is 5016718743.