I'd like to share my experience in communication with Booking.com stuff and their attitude towards customers.
Once I've been on a holiday trip involving multiple waypoints until my final holiday destination. Reaching my first waypoint which was Warsaw I felt ill with high temp and stuff and it looked like I can't go further at least next day and have to stay in bed at least extra day to try to get better. So my family went away to spend beautiful and sunny day in Warsaw while I, being in bed and drinking antibiotics, took the telephone and looked into our list of different reservations on the way to to Croatia.
All the bookings looked like a total mess for me so I decided to contact Booking.com service to check what I can do in this situation.
I was absolutely amazed by the service and stuff attitude I've got, it was like calling to your fluffy mother! The Booking.com assistant told me not to worry but to relax and wait till she will check everything for me and report.
The assistant made everything to make my trip as nice as it was in the beginning, she contacted all the places from my booking list and re-booked everything, moved it it a day forward, cancelled (without any penalties) those reservations which cannot be modified, and offered me something else.
So being in a similar situation do not hesitate to call Booking.com service they will treat you in a best way they can and all the problems will be resolved.
And they speak many languages! There is a big chance you'll speak to the assistant speaking your native language!
Thank you, Booking.com!