Very disappointed client of Superbalist

I was provided with a voucher code 'EXTRACHEER' which clearly stated you receive an extra 10% across departments. I duly performed my purchase selecting items i wanted. I only noticed that certain items were not discounted. I didn't give a second thought if looking at the price of individual items because this was a large retailer and assumed the discounts were in order. To my dismay when looking at the total were was a discrepancy of R163.50. How could a large retailer like this cheat it's patrons. I'm certhere are others who have been cheated.