Hi Which theory will be the best to manage this situation bellow?

Several employees experienced bullying from another colleague, who consistently belittled them and questioned their competence in their roles. Despite multiple reports of this behavior brought to the attention of management, the management chose not to take any tangible action aside from holding meetings where they asserted that such behavior would not be tolerated. However, the situation persisted, leading some employees to ultimately decide to leave the company due the toxic environment created by the ongoing bullying.

For example, you can include one theory from within each of the following: the classical viewpoint (e.g., scientific management theory), the human relations approach under the Behavioral viewpoint, (e.g., Maslow's hierarchy of needs theory), and Evidence based management under the quantitative viewpoint.