Booking.com complaint: Booking doesn’t protect his costumers

I booked a budget accommodation in London Golders Green with bed reviews, but for logistically it was ok.
The pictures showed on booking showed a decent property and with very little advance during the London marathon I had no particular demands other than to have a good connection with the airport and other transports, a bed and a shower.
Before my arrival I tried to contact che host several times for check in reply but didn’t received any answer before my arrival at the flat. Once I entered the property I found a squalid and indecent situation, unsafe and unhygienic. Rubbish everywhere and pieces of forniture even glasses disassembled in the entrance and corridor. The toilet door had a broken lock, toilet filthy with faeces and vomit, even a syringe on the floor, the shower broken, hair in the sinck, hair in the bed, power sockets disconnected from the wall, the room window could not be closed and no curtain. Pictures on Booking.com were completely different from what I found. I opened a complaint and booking replayed that the host was not willing to refund so they just apologise