False advertising

Yesterday morning at 11:28 I was at Shoprite Liquor Black chain Baragwanath in Soweto. I was buying a single court of Stripped Horse Milk Stout. Where the milk stout price tag read R19.99. When I got to the till to pay the price was now R21. 99. When I asked why the price difference I was told it was for a different product. When I asked why the incorrect price tag was plaed because that is false advertising, I got no response.