Wrong pricing

I purchased beef sausages at Lillie’s quarter store yesterday assuming that it was on the 2 for R80 special as that is what the sign in front of them stated. Once I got home and checked my slip I noted that they were infact bangers and were charged at R69 a pack. I tried to return them today to get the correct product and Woolworths refused as it’s a meat product. I find this unfair as I had the slip and the meat was exactly as I’d purchased yesterday.