Silence can be golden in the customer service sector. I think this smells like hourly reduction retribution as a means to give you a warning and not a dismissal for insubordination.
I think insubordination might be an inaccurate word. The OP didn't willfully intend to disobey his supervisor when he yelled at him in front of a customer. He had the best of intentions. And it has since been pointed out that he has suffered a great, personal emotional loss. He doesn't want someone else to get sick or lose their lives over something simple and preventable.
However, that incident and also then asking here if he did something wrong, showed he maybe doesn't have good judgement in this area (yet,) and maybe lacks emotional control at times. He's willing to grow and learn since he is asking questions.
All this may be what has been noted on his record. His superiors may have lost trust and confidence that he can do a front facing / customer interaction job at this time, when there are so many different types of scenarios that come up between customers and cashiers and management can't predict what may come up.
I agree with the recommendations of these posters:
How do you get shifts in the cashier position instead of bagger? By doing the job you currently have really well. By being a team player. By not yelling at a supervisor in front of a customer. By acting professionally.
And I would also ask for more cart/bagger hours. It's more important now for you to be in the store working and showing your commitment than being placed in the cashier position every time. Offer to fill in any spot (is there another job that is always understaffed that you can also train into?
OP, you want to win back some faith and confidence with your superiors that the outburst was a one time incident. That you know not to do it again. That you can be trusted in your interactions with customers, going forward. You do that by showing them through your consistent actions in knowing how to treat customers and fellow employees.
Even if you are a bagger, greet people, hand them the bags or place them in the carts and tell each person, "Have a good day." If there is a price check to be done and a second item has gotten from the shelf to scan or price matched, offer to get the item for the cashier. If you have to look at the price sticker on the shelf, take a picture of it on your camera to show the cashier and the customer. The more you show you can politely and effectively get along with customers, and that you are a great asset to the current cashier on duty, the more the store will want you to be working. The faster they put the past incident behind you. And perhaps they will give you more shifts as a real cashier and not just in name only.
