@skieurope , are you aware of this thread? http://talk.collegeconfidential.com/sat-act-tests-test-preparation/1987200-act-testing-wrongly-accusing-cheating-2017-p1.html
It is impossible to win an appeal, and it seems no one has been successful.
I personally know a woman whose son’s freshman year in college turned into a nightmare when ACT accused him of cheating, while he was already at college, after getting a substantial score increase on his ACT. It would appear, that for whatever reason, ACT is flagging some students who have substantial jumps in scores. I don’t know enough about each individual situation detailed in that thread, but it is clear that this is not an isolated case. I advise students not to take the ACT until they are thoroughly prepared to take the test.