My Booking.com Reservation Canceled Without Notice, Lost ₺14,000

I booked a 7-day stay in Cologne, Germany through Booking.com yesterday for my son and mother, paying over ₺14,000. When they arrived at the hotel, no one was there, and the contact number provided wasn’t answering. They were forced to pay 300 euros to stay at another hotel. This morning, I received an email saying the reservation was canceled, and they only refunded ₺700. Now I'm out ₺14,000 and left with no accommodation. This is completely unacceptable! Booking.com needs to resolve this immediately and refund the full amount. We are now facing a serious issue with finding a place to stay.