Bad customer service and arguing with customer

I buying my son boxed juice at picknpay protea north the price on the shelf was R3.99 at the till point was R6.99. the front line supervisor checked with and was there and she told that was the wrong price and it was under the juice she told me about barcodes she refused to give at that price. They call the manager he told me the same until I told them about PCA rules and I was recording the argument, that's when they gave me at that after 30min of arguing with me the customer.