Overcharged at Spar

I bought some stuff at Spar Brackenfell corner today, but when I got home I checked my tillslip, which I never do, but it looked a bit much for what I bought. They've charged me for 2 whiskas catfood of R115 although I only bought 1. I went back and showed them the slip. They told me to wait they have to confirm on the camera that I only bought 1, but said that they trust me 😡. I felt like a ********. I am a regular their and probably buy there 3 to 4 times a week, but I will rather buy somewhere else in future. They could have taken my particulars, asked for my ID and checked the cameras without telling me that they have to check. Buy Buy Spar.