If the case is as you mentioned, the money those agents have earned through this
discount is considered ill-gotten money and betrayal to their companies. Your cooperation with them on this discount is Haram (prohibited), as it is considered cooperation in sin and transgression, which Allah (Exalted be He) prohibits in His saying,
Help you one another in Al-Birr and At-Taqwâ (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allâh. Verily, Allâh is Severe in punishment.
You should repent and ask forgiveness from Allah (Exalted be He). (Part No. 14; Page No. 266) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.