Booking Nightmare: Double Payments and False Cancellations

I booked this property via the booking.com site and immediately received a message from the owner stating that she didn't understand how the booking went through as she is fully booked. She then proceeded to say that she could however accommodate me if I made a payment (more than the amount already paid via the app) into her account directly. I declined on the basis that I had already paid and couldn't pay more. I requested a refund via booking.com which she said she would authorise on her end, only to find out that she didn't and instead told booking.com that I opted to cancel.