Incorrect charge of items on special

Went today to pick n pay Uitenhage. Took some of there specials. Didnt check slip. When i got home i once again was charged incorrectly fr a few of the goods i bought on special. Tried to communicate on whatsapp. However no luck. This is not the first time. So frustrated. Petrol is expensive and i cant go back everytime to correct pricing. Im done wth them because they dont even have the decency to apologize.