Difference between advertised cost and cost charged

I have sent the complaint to ***, but have received no response: I am trying to place an order on Checkers 60 but there is a problem with the advertised amount and the amount charged Krush 100% Orange Fruit Juice Blend 1.5L advertised as: Buy 2 for R85 When I order 4 the cost shown is R199.96 iso R170 Chips Potatoes 2 KG R39.99 on order it goes to R44.99 What is the problem? It looks like an attempt to cheat your buyers.

Chris Smit