Incorrect Billing

Yesterday on the 02 August 2015 I bought some staff at Shoprite in Alberton. I bought 10kg R/B Rice and it was marked R79.99 and when I got home I realized I was charged R93.99 and same thing happened with the 250ml Vaseline Krayons, it was marked R16.99 and I was charged R22.99. I want my refund because I was billed incorrectly.