CHARGE FOR ITEM I DID NOT REQUEST & REFUSE TO REFUND

When I reached the Seat Selection page, there was an option to purchase an empty seat next to me. I did not choose that option. I took a window seat at a cost of R50,00 and noticed that the passenger on the aisle had purchased an empty middle seat. When I received the Invoice, there was a charge of R652,17 plus Vat for an empty seat. The Call Centre advised me that I am sharing the cost with the aisle seat passenger. I never agreed to do that! I asked for a refund and was told that I can only receive a voucher. This does not suit me at all, because I forfeit my Discovery Vitality discount of 40% when applying a voucher. I want a credit on my credit card!