I made a reservation to property Seagull 508 through Booking

I made a reservation to property Seagull 508 through Booking.com for a stay in Margate from 29 Dec 2023 - 3 Jan 2024. My free-cancelation agreement was up to the 29th of November, 2023. I had to change dates and location due to one of the travel partners' work dates. I then canceled the Margate reservation on the 26th November 2023, 3 days before the cut-off. The property refunded me but it was R500 less, and when I enquired, they indicated that this was their agreement with Booking.com. I then made an enquiry about it with Booking.com since my agreement with them was that I had free cancelation until 29th Nov. More than a month later, Booking.com customer services has still not come back to me about this issue, and I'm still expecting the rest of that refund.