Error from their side

I went to Woolworths at Sanridge last night to buy pork, when I got there the meat had the 30% discount only to get to the till and the lady told me that they can not sell that meat because there was an error. So my point was whose fault was it that the sticker was placed on the wrong pack, the manager/supervisor told me that there is nothing that they can do and they can not sell the meat to me.