@ClaudnDaye Geez, sounds like some real horror stories. It sounds like to me you’ve been going to the wrong dentists.
It is VERY unusual that I wouldn’t know a tooth would need a root canal before the filling is started, and it is very unusual for a tooth that just needed a filling but then needed a root canal would fracture irrestorably. I don’t want to toot my own horn, but I can’t even remember the last time I had a patient in pain after a filling.
I’m really sorry you’ve had these problems, but you need to find a more skilled dentist.