Poor customer service 😢 leaving customer stranded

I booked a self catering apartment for 10 days in Sandton to write my exams via booking.com named Marley & Katherine Apartments. These are residential apartments not self catering. When I got to the property I realized it did meet my needs especially since I'm there to write exams. I notified the property owner that I'd please like to cancel they referred me to booking.com since I booked through them, booking.com tried contacting the property with me on the line, the property didn't answer. Booking.com said if the property doesn't answer within 24 hours ilk get my refund free of charge, this was Sunday the 9th, I contacted booking.com on the 12th still the property didn't answer & today Friday they say they will refund me 15%...? Really? I didnt even stay there, I waited for 5 days for a refund had yo book alternative accommodation that will suit my need, I really need the money to book for my other 5 days ... please help me... as for booking.com they keep hanging up my calls when I ask to speak to the manager in charge