Basically there are two options here:
A) There is some amazing flaw in ACRs system, which nobody else have discovered before, despite the site having operated for decades and several forum members including myself having played there.
B) You made an honest mistake by misunderstanding the situation and thinking, you were on the final table, while in fact there were two tables left.
Which of those do you think sounds more likely, if you try to look at it just a little bit objectively? There have also been many posts from people, who thought, the software rewarded the pot to the wrong player. But every time it has turned out, they misread something, or they did not know the rules of the game, they were playing (e.g. shortdeck instead of regular hold`em).