If you are cheated of 20 thousand yuan because of the Book of Changes, you should call the police immediately. When calling the police, provide as detailed information as possible, such as transaction time, place, method, description of the people involved, communication records, etc. At the same time, keep all relevant evidence, such as transfer records, address books, chat records, etc. , which is helpful for police investigation. During the police investigation, avoid personal contact or trying to solve the problem to avoid getting into more trouble. Moreover, you can also consult legal professionals to learn more about ways to protect rights and relevant legal advice. Remember, reporting the case in time and preserving the evidence are the key to recover the loss.