Allegation of AI Use in Assignment

I am reaching out to ask for advice and guidance regarding an issue I am currently facing with my assignment . I have been accused of using AI to write my assignment, which I did not do. According to the university, the evidence for this accusation is the lack of quotations in one of the tasks, where the professor had mentioned during the lesson that quotations were not necessary. Based on this, I did not include any in my submission.
Another reason given is that I used sentences or phrases they didn’t expect me to use, possibly because English is not my first language. I am unsure what exactly this means, and I’m unsure how to respond to it. Furthermore, I have been told that my reference list was incorrectly formatted, which may be true, but this was not due to AI usage – rather, it is one of the most challenging aspects of writing for me, and I simply made mistakes.
I can provide evidence that I did not use AI inappropriately to complete my assignment. Is not possible to prove that I didn't do something, as far as I know. I haven’t received any help from the university, or even the proof they claim they have that I did use AI. The email I sent to the Quality Team explaining how I was writing the assignment seems to have been ignored, as their response suggests they didn’t even read my message.
I don't know what to do. How to proceed with an appeal, or if I should even appeal at all, given the potential consequences of revenge for even daring to question their decisions? Could anyone guide how to handle this situation? What could happen if I do appeal, and is it worth pursuing? How to appeal?

I would get in contact with your Students' Union as soon as possible for advice specific to your university.