Some months ago a family member said something very hurtful to me. One short and very specific sentence. Now I tried to talk about it with them. They denied to have said it and got very angry at me for making that up. We both were not drunk or agitated in a way that we wouldn't know what we just said or what we just heard. It's also not about that I got something wrong or misheard. I'm convinced they said exactly that sentence and they are denying that. They are truly mad at me for wrongly accusing them because they are convinced they didn't say it.
How likely is it that I made this sentence up in my mind? Why would I do that?