an invoice which I dispute

I was booking a guest into my diary and when I completed the booking it suddenly said it was double booked.      I phone one of your operatives and told him what had happened.        He told me that he would find the guests somewhere else to reside.     At no time did he tell me that I would have had to pay for the guests to be relocated.  I feel that is very unfair for Booking.com to have to charge me for the relocation as this situation was no fault of mine.  There is a charge on my invoices for £28.00.      At the time I was booking my guest my diary had a vacant room.   My number is 1804763.       Christopher Bond