Booking.com Doesn't Protect Customers! Hotel Didn't Refund My Deposit!

I stayed at the hotel called Elegance Wien for 2 nights through booking.com. The hotel took a deposit of 250 euros 2 months before the stay and said it would refund it within 7 days after check-out. 7 days later turned into 14 days, then 14 business days later, but they still haven't refunded me, and they haven't responded to messages either. Booking.com customer services responded once and asked for the documents, but they did not return any messages afterward, and sending the documents did not help. How can such a situation be allowed? I demand my refund urgently!