over charged

I went to makro on the 23/03/2016 to buy baby Cereal and purity that was on special The infant cereal advertised 4 for R60 and 12 purities for R85.00 which means if you take both it adds up to R145.00,Anyway I bought those items and when I got to the till there was no packer so I had to pack my own groceries because of that I never checked my slip because now I was working for makro.When I got home I seen that total was R176.90 which I was charged individually for each iterm I mean does there systems not have the same function as click where if something is on special it automatically deducts on the till, its not alot of money but Im furious because I mean if I wanted to buy these items on normal price I would gone to clicks and not drive so far for the items