Diesel pricing

The different filling stations displayed a different price on the big advertising Boards that is different from the actual selling price at the pump. It is grossly misleading of the public as many users do not checked the price per liter paid. On 11 April 2018 I stopped at the Shell Rossouw street Motors, 205 Rossouw Street, Murrayfield. The price on the big advertising board for diesel is R13.82 while the pump price is R14.19. The supervisor poor excuse was the price of R14.19 is for 50 ppm and the advertised price is for 500 ppm. If a product is advertised at a price, the provider is obliged to give it to the customer at that price. Nowhere on the big board it was stated that the price is only applicable to 500 ppm or T&C apply. I noticed the same trend in the Lynnwood, Menlopark and surrounding neighborhoods. What does the Advertising authorities say about this misleading claims??