Bad customer service

On 14 Sep 2017@about 11, I had my worst experience ever @ pick pay Richardsbay. I saw a save slip for 1kg Megapack sunlight dishwasher tabs for R24.80. As I.knew this was a great bargain I took the slip with.the product, went to scan it to see if the price was correct then.went with the slip to the till, because the service is normally very slow to check the prices on the shelves. The first manager Selvy said she couldnt help me and called the manager Casual. They talked where I couldnt hear them and then he came and asked me: where did you get this, because its not from my shelve!!! I told him to go check his cctv cameras as that would show me taking it of his shelve.. he just carried on insinuating I got it from somewhere else and not his shop...even though the slip is identical to all his slips, saying save on the one half and then the price on the other.