Barry, Yes I agree. It is all very well for BdC to suggest that properties refund guests but it's not BdC that would have to cover the cost of this.
You should be able to edit your non-refundable rate plan under:
Rates&Availability/Rate Plans then click the arrow next to your Non-refundable rate plan and then there should be an edit button on the bottom right. If this is not there contact Booking.com as pibpmarco has said.
I have just added a non-refundable rate plan and its not working the way it should. Booking.com's system seems to be ignoring all the settings and just offering every guest a non-refundable rate.