Ostrich Promotion billed at more than advertised price

Visit Indigo Spur, Waterstone Village for a meal today - Ostrich Burger Promotion advertised on table talker @ R79.90, when bill came I was charged R82.90. I pointed it out to the waiter, who told me 'sorry I did not pick it up' but no attempt was made to rectify the bill. It was only R3 more per burger, but if they run a promotion, why is the correct price not loaded on the computer?