Wrong prices

Yesterday I was so excited with the 50 % clicks special, then I decided to take a Milk Frothier together with other things. Then I was surprised as the advertised price was R79 then at the tills the price was R99.99. then I asked the teller to come with me so that I can show him the correct price. Only to find the special is finished and they did not update their prices unfortunately the teller said there is nothing he could do about the situation. My point is why is clicks advertised with wrong prices to attract us and knowing that those prices are wrong.