Charging for extra items that's not there

I had to come lodge a complaint here because pick n pay doesn't bother responsing on their Facebook page. Their center point branch doesn't answer phone!! Been trying to call because I was charged for an extra packet of simba chips on Saturday when I only bought one!! They can also look on their cameras and see, it was at 13:40, I think till 3, cashier's name is Mancu J Mancu