Dischem East London - Manager harassment of customer

My mother in law purchased the almond milk special at Dischem East London on Tuesday and when at the counter placed one box on the counter and told the lady there were 4 more in the trolley. When it was time to pay the lady asked about the milk in the trolley and my mom repeated that she had told her. The manager was called and arrived She didnt even greet she simply said Whos fault is this. My mom in law explained what happened and she loudly repeated Is it your fault or her fault. The manager continued to moan at my mom in law about how she doesnt get to make decisions about stock and how they run her buisness. This all happened with staff and other customers looking on. The manager seemed to take pleasure in making a fool of a customer. This type of behavior is unacceptable from a person in her position. The situation could have been completely avoided and handled quickly and professionally. It is unpleasant and no customer, particularly a senior citizen should have to go through this.