I was charged R200 extra for earings I also cannot return

I just bought a pair of earrings at Stern Northgate today displayed R999, I paid with my debit card. When I checked my slip it read R1199. I informed the cashier who said the display price was incorrect. I asked for a refund altogether. I was told unfortunately they cannot reverse my payment because I paid with a debit card not a credit card and they don't have any cash in store. To tell you I am walking out of Sterns with the 'over charged' earings and 30 day to return them (however depending if there will be any cash payments during the 30 day period) This just isn't right. Please help