Anyone else being scheduled for a shift without ANY notice?

Hello, I'm a highschooler who has been working for Panera Bread for around 5 months and have recently started my senior year of high school. Since the summer is over I requested to work less hours and have updated my availability to fit my schedule. However, 2 days ago while at a school event I get called asking where I am and why I haven't showed up for my shift. I explain that I wasn't scheduled that day, and then my manager starts saying how I was. I check my schedule and it says that I was scheduled to work. BUT I know for a fact that 2 days prior that was not on my schedule. I had a big school event that day and made sure that I was not scheduled to work that day. Unfortunately, this is not something new, there have been times where I will see a shift pop up that wasn't originally there, but unlike this time I chalked it up to being that I just misread my schedule and still went to my shift. I'm not sure if this is some glitch in the app or if my manager is completely ignoring my availably but it's getting very frustrating. And to top it off today my schedule gets updated and I'm scheduled to work on days I specifically told them I was unavailable. I'm thinking of keeping screenshots of my schedule because unfortunately I didn't do that last time. Out of curiosity does this happen to anybody else? And if possible does anyone have any advice on how to deal with this? Thanks.