dilemma with my estranged dad and half-sister

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My family life has always been strange, at best, but recently something has happened that I don't know how to handle. My parents divorced when I was three, and my father remarried when I was four. The woman he married has always disliked me, but when my mother died a year after they married, she completely flipped out. Apparently I was a reminder to her that my father had loved someone else before her, and she abused me extensively until my teachers got involved when I was seven and told my father that he had to get me out of the situation or they would call the police, so I was sent to live elsewhere. My father and stepmother had two children during their marriage, a girl when I was five and still living there, and a boy when I was in 7th grade and living with my father's sister. My father has never been in regular contact with me (I have not seen him in 10 years or more), and I have learned to deal with that. Two years ago, my sister called me and wanted to meet. I had not seen her since I was 7 and she was two (I am now 29), and we slowly began to talk over the phone, then met in person, and we formed a relationship - my kids (aged 5, 7, and 9) even call her Aunt now. We made plans to go see her and her husband for Thanksgiving this past year; I switched shifts with someone at my weekend job so that we could go since they live in another state, discussing the date well in advance. Four days before we were supposed to leave, my sister informed me that she thought I was talking about a different weekend and the plans were off. I was upset and told her so; I sent her an email telling her that I was angry that she had not paid attention to the date sooner and the kids were very upset, plus I felt she was not respecting the effort I had put into planning the trip. She has not spoken to me since. I have tried to email her and call her, to no avail. I left her a message about a week ago letting her know that our father's sister is not in good health, and that night my aunt called to tell me that my father had called her to see how she was feeling since he 'heard' that she was not doing well. I am at a loss as to what to do now that it is clear that she is getting my messages and communicating with our father, but both refuse to talk to me. Do I just forget my sister and accept that I will never talk to her again? What do I tell my kids? They ask about her regularly since they have become fairly close with her and her husband. Was I wrong to tell her that I was angry with her?