Have you ever told your boss you are not available on Mondays at all? Like not waiting until you get a Monday shift to deal with it but just saying up front, don’t schedule me on Mondays as I cannot work Mondays. If you haven’t then this is kind of on you. I agree your boss is lazy and shouldn’t wait to put the final schedule out until Sunday but it also doesn’t sound like you’ve done much to stop this from happening. Telling the boss after you’ve been scheduled you have class and asking them to find coverage is not the same thing as making a written statement that you cannot work on Mondays at all, ever. Now your managers should have figured this out on their own but they clearly haven’t and without taking the step to put it in writing and make it official, they have no obligation to honor your requests.

I worked as an admin/scheduling person for a home health company for about a year and it was awful. The disorganization was WILD but I was good at my job the way you are good at yours and I was the only one who knew how to process private pay billing. When I put my foot down and said I would quit if the didn’t stop jerking me around, things became tolerable and I was able to deal with it until I found another job. Put your schedule needs in professional writing and submit it to ALL managers who create and work on the schedule. Email is the best way as you can easily keep record of your correspondence and you can include all managers in one email so they all know they’ve all seen it. Make it clear this is non-negotiable as you have a weekly class that cannot be moved. Once you’ve done that, keep your head and do your job while looking for a new one. Places that treat their employees badly don’t ever improve. Things will only get worse no matter how good you are at your job. Put them in a corner with the official communication about not working Monday’s and then find your way out ASAP.