Correct, contracts dont trump laws and your extreme example would not fly in court because of it and because it would break humantarian laws and rights agreed upon in our countries.

That said, he speaks the truth. If a contract says you earn x and you earn x+20 euro, they can and will compensate for that 20 euro. Its perfectly legal and ive seen 2 euros go down from my pay because of book keeping errors. However, i assume the law has a margin for book keeping errors, and if not they can demand it back in court. You signed on it after all…