Extra Shift Tomorrow

I'm going to preface by saying that I know full well that Walmart does this. It just feels different to experience it than to hear about it.

I found out an hour ago (9:45pm) that someone added me for a shift from 8:30 to 5:30 tomorrow. I had plans tomorrow, including an appointment, that I had to cancel. I considered calling out, but I'm still building my PPTO back up from being sick last month, and I can't really afford to not go in, considering that they took off a day next week. The worst part is that the notification said it was a day ago, so technically, they gave me 24hr notice. Not that I could really do anything if they hadn't.

It's just so frustrating, considering that I work hard. I'm always trying to help people, I'm always friendly and polite to customers, and I always try my hardest. Again, I know it's Walmart tradition to treat people who do that this way, but still.

I fully intend to make my feelings on the subject known. Will I get brushed off? Yeah, probably, but I'll feel better.

If anyone has some actual advice about this situation, I'd greatly appreciate it.