Statutory, by definition, is a term which notifies policies decided by law. Statutory compliance abides the organization with certain law which needs to be obligated to function within the legal boundaries.
Mandatory, by definition, states the obligation that is imposed by law amended by the government or by the organization. A mandatory law requires the employees to follow rules which are amended by either the government or any private community.
For instance, any employee has to follow the terms and conditions which are amended by the HR team of the organization. To put in simple words it is mandatory to follow statutory compliance to maintain a legal functioning of the organization.