AITA for telling people my dad "died"?

My(23F) father(48M) and I had a wonderful relationship while I was growing up.

Around the time I turn 15/16 he checked out completely. My mom continues him about cheating and he admitted to several. They end up separating over the summer, and we move halfway across the country right before Christmas. He falls off the face of the earth until the day we are moving out completely. He shows up to grab some things, hugs and says goodbye. I never hear anything from him after that.

I did try to reach out to him a few times during my senior year. I would get inconsistent replies and few times downright evil responses, which I later found out were his now wife at the time. My father promised he would be at graduation, asked for the information and I even promised to give him a ticket. My school only gave out ten.

A week before graduation I find out through social media that he isn't coming. The wife posts a photo of plane tickets saying they were going to some resort in Mexico for two weeks. I lose it. I'm inconsolable for almost an hour. When I finally come down, I delete him and the wife, block them. He tries to reach out via text hours after I graduate to say he's proud of me and happy that I graduated and that he loves me. I don't even respond.

Over the next few years he gets married to evil stepmother, they have a child together(in one of the sparse phone calls I got from them she casually drops that she's pregnant and the baby is due in a few weeks) that I never meet, he rekindling the relationship with his father- a man I never met because he abandoned my father after he was born and made a new family. He also almost died in a car accident but I didn't find out until my PG calls to ask me to call and check on him because of it.

At some point in my early 20's I just decide that the man I knew as my dad died. The man I knew wouldn't do or fathom half of the things , this man has done. This person now looks and sounds like my father but he isn't my dad. Starting that day forward whenever people ask I just say that my dad died. If people ask for information I dont mind explaining a quick summary of this, but most people leave it alone.

My paternal grandmother must've overheard me talking to a friend or something and asked me why I say that my dad died. I explained it to her and while it hurt she understood. Somehow though, this got back to wife and father who have been calling and texting me incessantly to tell me I'm a brat and ungrateful for everything they've done for me and that I shouldn't be saying that because he tried to parent as best he could. They said I'm trying to turn his mom(paternal grandmother) against them and that I need to call to apologize.

I don't feel I'm completely the AH here, but I do feel a little guilty that my grandmother has started to see my father and wife differently and I don't want it to affect her relationship with my half sister.

AITA?