My best advice is to gather documentation for everything that happened and to ask the adviser who had supported you (even if they are now at a different university – that’s what I’m gathering from what you wrote) to write you a letter of support to verify your story. Who is your adviser now? Who is on your committee? Who taught you in those three classes?
You should be able to make a case based on the fact that you were allowed to go through the program – that’s on the university, not on you. Also - if you were allowed to retake one of the courses in which you earned a C, shouldn’t you just have two Cs on your transcript, not three? Can you negotiate a deal in which you retake the other two courses?
Exactly where are you in the program right now? It sounds like you’ve just taken comps, so you haven’t written your dissertation yet? Absolute worst case scenario, would it be possible to apply to a different program, perhaps with the support of your original adviser, and continue there? You might have to take some course to establish residency and retake comps, so it would cost you a couple of years of progress, but at least it would enable you to finish a Ph.D.
I agree with @thumper1 that it would probably be best to contact a lawyer. But if you end up staying in this program, you don’t want to burn so many bridges that it would be difficult to get support from faculty mentors when it comes time to apply for fellowships, grants, and jobs.