Cancellation by booking.com without permission from establishment

A guest asked for a refund at 6pm on the night of arrival which totally contradicts the cancellation policy. I received her request via email from booking.com. When I clicked on 'Respond' I was automatically taken to a page on booking.com that declared her booking had already been cancelled and she would be fully refunded WITHOUT MY PERMISSION. When I immediately contacted booking.com to tell them they had cancelled this booking WITHOUT MY PERMISSION, they claimed I had done it, that I must have pressed a 'wrong' button, that the extranet said I had cancelled it etc etc....The fact that I would not refund a booking made by a guest just because she did not feel like driving that day and cancelled on the night of arrival and that my cancellation policy was clearly accepted by her when she made the booking payment, suggest that booking.com over rode my policy and keeps its telesales people in the dark as to how it really operates behind the scenes. I have sent several messages to them asking for proof of the cancellation from my side, but they cannot furnish it because it doesn't exist! If booking.com really wanted to honour their contract by hearing my concern that this serious issue proved there was no protection for accommodation establishments keeping places reserved for a guest, only to have it cancelled at the last second and fully refunded to the guest, then they would have transparently engaged with my lodged complaint. Instead they have backed out and provide nothing other than an endless series of different telesales people spouting the same script. To all accommodation establishments out there, let this be a warning to you; booking.com makes you feel you are in control of your listing and has earned a fat 19.6% commission off your bed nights, but in return, they control your listing with utter disregard for your policies and will cancel a booking you have held for a guest when they choose without your permission or knowledge. Listing on booking.com is high risk.