Ai has ruined my university experience

I'm sure this has to have happened to many people. I'm in university. I love to study, I love to write essays, I love to take notes, I love all of it. I truly put a lot of effort into my work. Recently all of my assignments have been coming back ai generated. The first time was for a final essay weighting 40%. I failed it and almost failed the class a result. The next was a minor assignment that didn't have as much of an impact, but still annoying. I've started putting all my work into ai defectors and they all say like 82%, 75% etc and I don't understand WHY. I don't use ai. I detest ai. I have a family friend who used to work as an assessor and she said Turnitin (the ai detector used here in New Zealand) is incredibly inaccurate - yet they continue to use it. I'm just so put out from all of it that I just want to drop out. I'm sick of looking like a cheater, and I know none of my tutors believe me when I say I don't use ai.