Something like this happened to me the first time I used booking.com... but around 10 years ago. Someone got ahold of my booking details including the property name, booking number, etc.. and then contacted me via a spoofed email that looked like it was from booking.com, and another email that looked like it was from the hotel and asked for the reservation to be paid in full by bank transfer. A while after making the payment, I thought about it more and checked the email headers from the booking.com email and became more worried after finding some odd things, which I can't remember now. I contacted booking.com and they confirmed they did not send the email asking for payment. Long story short, booking.com did fully compensate me, around 800 eur. As for how this has been happening for 10 years, one guess is scammers could be using packet sniffing to intercept booking details sent from booking.com to hotels which could be using unsecured email protocols.