Hi bpbreakout,
First, I want to say that you are not alone in facing such accusations. Me, too. When H is dysregulated, every expression I have is wrong. If I blink too much, I'm disrespecting him. If I look at him wide-eyed without blinking, I'm looking hostile. It's not me, you know; it's him. I can look exactly the same as I did the moment before and suddenly he wouldn't be ok with it anymore.
I think it is worth thinking whether your expressions did cause some problems. pwBPDs are very sensitive (sometimes hypersensitive) to emotions, so they may detect things even if you're trying not to show them.
Her saying "you don't care about me", though, is just a way to lure you back into the conversation, because you mentioned you have stopped responding (which is good- you cannot win). Remember don't get lured into an argument about whether you are about her though, otherwise you will be defending yourself on two things at the same time, and the conversation will just get out of hand!
Take care.