Is it permissible to inform the general manager about his children's discriminatory treatment between the questioner and their secretary, knowing that he was previously aware of this, and is this considered a fitna (strife/discord)?

If you are wronged by the manager's sons, you are permitted to complain and seek justice from whoever can grant it to you, whether it is the manager or someone else, based on the Almighty’s saying: "Allah does not like the public mention of evil except by one who has been wronged." This seeking of justice is not considered forbidden discord, because it is the right of the wronged person, according to Islamic law, to seek justice, even if it involves backbiting the oppressor.