Cancelled but paid Reservation

I am relatively new but very confused and find that it cannot be right.  I had a guest who cancelled after apparently finding out that very morning her son contracted covid. She cancelled later in the afternoon but didn't actually cancel as such so I was told by booking.com staff but sent a message to me and to the platform. She asked if I could give a refund given the circumstances and I said I am unsure how the booking system works in this situation but I am sure we can work something out and she must contact them. I also contacted them as I wanted to find out what happens and they had advised me that they were sending a request saying that I agree or denied to cancel for free and I denied for free due to my policy which is cost 50% of booking. I wasn't too kind I know but I am only a small new business and I know this lady is lying as she had clearly stuffed up in messages she sent me that day and I know it had to be her and her family looking at my property (I have external cameras)3 mins before she sent me the oh no have to cancel message. Anyway after denying free cancellation I phoned booking.com to make sure that they put the unit back up for availability at least for the second night so I could get a guest in to cover that nights booking(second night). They said ok they would talk to guest and make sure they have cancelled and then make my unit available. The unit did not come available on the platform sadly so no one could book. I phoned booking.com after this and they said she never cancelled so full payment is given.  Well the whole 2 nights minus bookings commission was transferred to me.  Now they are saying that my policy is 50 % and so she can only be charged 50 % as she was a no show and I have to pay back the other half. Why should I have to pay as far as I am concerned I did everything right and booking.com were at fault for not making my unit available for booking like I asked and they said they would. How can I get help or them to understand this? I am upset not just over the money but that they are not accepting fault and therefore are not doing right for their clients like us. Is there something else I can do or could it be the miscommunication in language? Is there someone who I can ask to speak to who may help or is this simply a battle not worth pursuing?