Company wide time cuts?

I was originally a cashier when I first started a few months ago, an assistant manager approached me and asked me if I wanted to move to pick up. I told her yes but my only requirement was I at least be full time (40 hours+). I gave my lead my availability and everything was fine, but now we have a new store manager and for some reason she’s making the schedules. Ever since she started my hours have been constantly pointing downward. From 40 to 28.5.