Not happy at all to pay full amount on something that was on special and

i was at Shoprite Pimville Square and while doing my shopping i saw Future life on special at R30.00 and i took two expecting to pay R60 for both, because i was rushing to work i did not check my till slip but when i got to work i took out my slip to check and to my surprise i paid R79.99 for both SO my argument is how does till operators at Shoprite work?she was supposed to explain to me about the special but No she failed. instate she let me pay full amount. i am so not happy with Shoprite service. its not like i was been helped by a machine but a person who was to explain