Academic Breach of Integrity because of AI

I have just been informed that my grade is being reduced to 40 because they believe that my essay was AI generated. I received no prior warning to this, or any chance to discuss what was flagged in my essay or why. The email they sent me said that there is no way of appealing this decision, but that I can instead make a formal complaint. I don't know what to do- The essay that was flagged was part of a 24 hour exam in which I had to write two essays in 24 hours, and I stayed up and spent hours and a lot of effort into this work and they are capping my grade even though I did not use any AI. What can I do to prove this? Due to the essay being under heavy time constraints, I did not make an essay draft and just wrote the essay straight. The only thing I can think of is that I did use grammarly to help with my grammar, but I have dyslexia so my student support plan allows Grammarly to be used, and I am worried that this is what caused it to be flagged as AI. Please let me know what I can do, and who I can talk to as they penalised me without giving me an opportunity to explain. This essay is worth 85 percent of my overall module grade and I am a third year so this will have a huge effect on my grade. I do not have version history on word- I have heard a lot of people saying to use this and show time stamps, but I do not have this on my computer. It only came up as 8 percent AI when I submitted it on ZEROGPT so I don't know what to do.

This sounds extremely unfair. There's probably more that can be done so look at other users replies too. But at the moment definitely email your course office and ask them how this decision was made and what you can do to appeal this, have a note of your history (browser history) to show your research progress etc if needed. Reach out to your module leader to also talk about this and the next steps you can take. Reach out to the student union for help in the appeal process if needed. Arrange a meeting with your tutor regarding this too and ask them for advice/help. I apologise that it is a lot to do but first of all email course office, module leader, tutor, or/and student union.
In the meantime, definitely contact your wellbeing team and let them know about this issue so you can get the support you need in this stressful period and they may even be able to help you reach out to the relevant people. I hope that everything goes well and hope this helps!

I echo much of what has been said here.
Your academic advisor and university support staff won't be able to help with the bones of any appeal, but they can give you a rundown of procedure and the basics of what is required.
On the face of things, this is all very odd.

I have just been informed that my grade is being reduced to 40 because they believe that my essay was AI generated. I received no prior warning to this, or any chance to discuss what was flagged in my essay or why. The email they sent me said that there is no way of appealing this decision, but that I can instead make a formal complaint. I don't know what to do- The essay that was flagged was part of a 24 hour exam in which I had to write two essays in 24 hours, and I stayed up and spent hours and a lot of effort into this work and they are capping my grade even though I did not use any AI. What can I do to prove this? Due to the essay being under heavy time constraints, I did not make an essay draft and just wrote the essay straight. The only thing I can think of is that I did use grammarly to help with my grammar, but I have dyslexia so my student support plan allows Grammarly to be used, and I am worried that this is what caused it to be flagged as AI. Please let me know what I can do, and who I can talk to as they penalised me without giving me an opportunity to explain. This essay is worth 85 percent of my overall module grade and I am a third year so this will have a huge effect on my grade. I do not have version history on word- I have heard a lot of people saying to use this and show time stamps, but I do not have this on my computer. It only came up as 8 percent AI when I submitted it on ZEROGPT so I don't know what to do.