I got a subpoena and showed up to court and was canceled and nobody notified me. Need to go again but can't.?

A teenager broke into my husband's company truck so I called the cops on him. He got arrested and now his lawyer gave me a witness subpoena to appear in court. I showed up and the court was cancelled since the lawyer was attending a different trial. I was never notified of the cancelation. Now I have to appear in court again, but this interferes with my schedule since I have awards ceremony for my class that day. I called the lawyer and he said that was just too bad and that I have to appear if not I'd get arrested. Why should I be inconvenienced when I was not the one to committ the crime, it was his client. What can I do? I have to appear in the summer as well and this interferes with my vacation time!