Is my ex girlfriend testing me? Or just really dislikes me? I'm going nuts?

I recently wrote my ex an apology letter. I didn't say how I felt. Just apologized/empathized with her about not treating her as well as I should have. (I ignored her feelings). Said I hoped I could make it up to her and that I was working on becoming a better person. Her sister (whom I'm friends with) saw her a week or so ago and told me that my ex asked about me and said that she wasn't angry. That emotions make you do crazy things. So I thought that a letter could be a way to reconnect in some way. We were together for a year, and were good friends for a few years before that. We've been broken up for almost 3 months and have had very limited contact. All of which she has been angry with me. I didn't expect a reply to the letter, but got one! She just thanked me for the kind letter. I didn't respond right away because I was driving home. By the time I got home, she had sent me another text saying have a good weekend, I'll take your lack of response as a social cue. So I said sorry, just got home. Thanks for reading the letter. I told her I still thought about her. She said ok. Then said that until I have the balls to actually TALK to her that I could fuck off. So I called! She answered! I said hi, how are you? She said I'm great (angrily) I'm watching a movie and can't talk. Then hung up on me. Then sent a few more messages telling that just like when she wanted to talk I had to see a movie. I said no biggie. I'll call you tomorrow. She said don't bother. I don't like you. What the hell was that? She continued to angry text me a few more times. Saying she'll be cordial in public but she will never be okay with how things went down. Blaming me for some perceived distance between her sister and her. Months ago the sister got involved against my wishes. Telling my ex that we should settle our situation out. That set off a whole night of angry messages from her, but a week after that she texted to say that her sister and her were cool again. I don't know what to do..
Is my ex girlfriend testing me? Or just really dislikes me? I'm going nuts?
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