Meh. They are just terrible. We once booked a hotel with a children's bed, which was advertised as an option on Booking.com . When we go there, no bed, and they could provide one. After much discussion, they allowed us to cancel the room and they would refund the 125 Euro.
Except the refund never came. So, we contacted booking.com and have been passed between support personnel for months. At some point they wanted months of our bank transcripts (which I rejected because of privacy issues, I don't trust such a company to securely handle/erase them). After five months, we just accepted the loss.
(Customer service can be good. E.g. recently Apple double charged Apple Care. I had someone on the phone within minutes and I got a personal contact within their financial department that I could message or leave voice mails for. They were very helpful in the whole process of getting the money back.)