Supermarket knowingly overcharging

[GatsbyNZ]

So 8 or more weeks ago, I noticed that the item I bought from a supermarket was more than I thought the price had said. The second and third time I noticed I brought it to the attention of the checkout supervisor they said they would pass it on? The 4th time I asked to speak to the store manager (medium sized main chain), told them i had already told the store but nothing had been done. 3 or 4 weeks later, bought the same item and still being overcharged by 50p. The floor manager told me they know about the problem but it is too difficult to fix and they are working on it. The floor manager offered to give me the item for free, but was hesitant to give a phone number I could ring to complain. If they sold 20 of these items a day, they would ripped off the customers by £560 in those 8 weeks they new there was a problem. Should this be reported to consumer protection groups. I want them to make a donation to a charity for the value they have misled the consumer by. Any thoughts?