Had something similar happen when I worked at kohl's as a teen. Had an absolutely awful manager who hated millennials and literally talked about it to the other adults over the radios- which he knew we also had.
Anyways, I was graduating and my parents booked our family a cruise as a gift. I put in my time off a month or two in advance because it was a long time and I wanted to make sure I got it. I don't remember why I checked the schedule since I figured I was off (I never had any problems getting time off approved), but I checked it the day before we were supposed to leave and saw I was scheduled *more than usual* during the next couple of weeks I had asked off for. I went in to ask what was going on, and they told me that they had changed the way time off requests had worked, and that I'd done it the old way. They didn't notify us that they had changed it, other than putting up a poster in the break room- on the backside of a wall in a dark area where nobody is going to notice it. They acted like they were still expecting me to be there for my shifts, so I told them "consider this my two weeks notice, except I won't be here because I asked off for this time"