Unfounded PIP....totally mismanaged

[Not taking it!!]

ill try to keep it brief. My boss snapped at me a year and a half ago that I make too much money. I am the oldest and do make more than the rest. They methodically got rid of seasoned employees and now only hire very young, for cheap. I was blindsided with a PIP— no prior warnings, write ups, even conversations. No reviews for 4 years. Misinformation in the PIP, my manager doesn’t communicate as outlined. I did everything they required for the 90 days, but it’s all subjective. Now they increase it to 120 days Because they can’t decide if I’ve passed or not. Just more mental torture. What to do??