Older ladies leave half their items on my belt because "I was taking too long"

I work as a cashier a fairly large grocer, and although the one 10-15 minutes away from the one I work at has a much bigger selection and looks a whole lot better than mine, mine is pretty much always busy. Probably not busy as a lot of you guys here would consider, but as I'm fairly young, (18) this is my first job, and I have an anxiety disorder, any type of "busy" messes with my head at least a little. This story will be a little fuzzy, due to the fact that when a panic attack flares up (which, this job gives me frequently) the details during that time are very blurry.

So, I'm at my register. I've worked here maybe a month at this point, when I'm checking a nice older man out, and realize that my line is now about six people long, with only one other register open who is just a little less packed than I am. Obviously, a panic attack sets in, but I do my best to keep my calm and check everyone in the line out, most of whom could see my stress and were very kind about it. Three older ladies walk to the register after putting their items on my belt. Their crew is composed of age 50-something large women who all look like they have a stick up their backsides, and their leader as it seems, is a lady of about sixty. The other two don't really talk to me, but the older lady does, so I'll call her OL for "old lady".

Now, I'm checking them out and doing the mandatory "smile and greet" stuff, and they just give me this look of annoyance the whole time. Now, since there are three of them, and there's like a four-foot gap between a fair amount of items, I assume that they mean to pay for the things further back separately. This is how this goes:

Me: "Okay, that'll be [total]"

OL: "Excuse me? We were talking, before you rudely interrupted us."

Me: "I was just telling you your total, ma'am, it's [total]"

She looks at me as if I had just insulted her.

OL: "Fine, here."

She slides her card, and I start going through all of the prompts on my screen.

OL: "Wait, what about all that stuff back there, you get that?"

Me: "No, ma'am. There was a lot of distance between the items and there was more than one of you, so I thought-"

OL: "Well hurry up and scan them!"

Me: "Sure thing, ma'am, I just have to cancel all the payment stuff, give me a minute."

OL: "What are you doing now?"

Me: "I'm sorry ma'am, but when I hit the "total" button and go through the prompts, I have to-"

OL: "You know what? Forget it. You're taking too long, just ring me up for this stuff."

I ring her up for the things I already scanned, she gives me one last look, and leaves. I ask if they're not buying the other fifteen or so items on my belt and they say "No, we don't have time for you." or something along those lines. So now I'm standing there, dumbfounded, with 15 items that need to be restocked on my conveyor belt. It's near closing time, so after this exchange, the store is pretty much dead, and my line is empty, so I turn out my light and call CS over.

Now, I've never actually met my manager, as he works during the day, and I get the afternoon shifts, but pretty much everyone who works at customer service has authority over the cashiers, so I have several bosses. I think total I have about six, but no more than three are usually there whenever I work. One of the three, however, are in a slightly higher position.

I don't like calling them unless absolutely necessary because of my anxiety, as I don't want them to think I'm stupid or incompetent or something like that, and at this point I have a general fear of them, as I don't know them very well other than the fact that they can take away my job if I mess up.

The higher up of the three on duty at this moment comes to me and I explain the situation, to which he says "Oh wait, was it three older women? They asked me where something was, and when I told them that it wasn't in stock, they called me stupid. Sounds like they acted like f@cking b!tches to you too. Don't worry about putting the stuff up, the store's slow right now, I'll take care of it for you."

Thank God for really cool bosses.

I've had plenty of other experiences since then, but this was my first, so it holds a special place in my heart.