Do I have any legal rights if my employer assures me that they can help me with a scheduling issue but later holds me responsible for not working?

I am a student and work part time for a major hospital in Ohio. I have worked for the company 8 months. I attend college full time. My manager and I discussed my upcoming schedule and I was assured that he was willing to help and work with my school schedule. Generally, the work schedule is posted in two weeks increments, on this occasion it was posted a couple of days later before I was able to give him my school schedule. I was told to call off each day that I was scheduled to work. Now I am being penalized for excessive time off. My manager said to me that he had given me the wrong information about attendance. I know what the attendance policies are. If my manager had not provided me with misinformation I could have made other arrangements to protect my future with the hospital. I have met with the HR department, they agreed that other measures should have been taken but I was told that it is solely at the discretion of the manager if I am held responsible for the call- offs.