You cannot take any action in this case. Merely signing the appointment letter does not make the candidate an employee of the organization. For any action to be initiated, there must first be an employer-employee relationship. In this situation, since the candidate has only accepted the Appointment Letter and not joined the organization, no action can be initiated against the candidate. At most, you can blacklist that candidate for all future appointments in your company or group companies.
Regards,
Rakesh Pd Srivastav