Maybe he thinks that it's not worth the effort. Putting her in jail or having her fined for 6,000 baht won't bring his millions back.
Section 341 of the Thai Penal Code:
"Whoever dishonestly deceives a person by falsely representing a fact, whether past, present, or future, or by concealing a fact that should be revealed, causing that person to act, not act, or allow something, and thereby causing harm to the property of the deceived person or another person, commits the offense of fraud and shall be punished with imprisonment not exceeding three years or a fine not exceeding 6,000 baht, or both."