Refund on car rental.Drive South Africa

I cancelled car hire on the day of collection.I was supposed to be charged a 2 day car rental as stipulated in the voucher.But the company would not refund me back for the remaining 3 days of the rental period.All they are stating is cancellation policy during the pick up period of 15th December to the 4th of January 2020.Please assist as I am supposed get my refund of 3 days out of 5 rental period.Thanks