Disgusted with Shoprite staff

On 8 June I went to shop at Shoprite as they had a massive sale on various items. I purchased milk at R54 X4 6 packs and lots of other goods too. When I got to the till I took one 6 pack out of the trolley and advised the cashier that there are 4 X 6 packs....she carried on scanning as I emptied the trolley...when she finished scanning I paid and left, at the door on my out the security picked up that I only paid for 1X 6 pack. The security called the manager and she then took me to the cashier that assisted me to hear what had happened....later I paid for the other 3 packs and went to the office in Shoprite... the manager called the branch manager who could not even greet as she entered the office and they interrogated me and was not willing to listen to the cashier. I spoke on the cashiers behalf to say that the lady made an honest mistake as she was busy scanning goods and packing as there were no packers. I wrote down my statement and the asked the cashier to immediately cash up and further matters will be dealt with. I said that I would bare the brunt for her to keep her job but then they said that I must then get locked up. They had no intention on giving her a second chance and also have no way of speaking to their staff. They said that they must stay consistent by following procedure. I agreed however I advised that they must teach all cashiers there to be consistant and advise shoppers to empty their trollies completely. I bought bulk milk there before and never did I have to remove all the milk from the trolley, the cashiers advises to only give one to scan. The manager has ni way of speaking to people including customers.