It is not permissible for you to
cheat. Your conscience will only be clear when you tell the truth about the number of bottles that are delivered every month. If you do not do so, you are cheating your agency and being sinful for cooperating with the contractor in sin, transgression, and taking undeserved money. Allah (Glorified be He) says (what means):
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.
(Part No. 13; Page No. 208) The fact that many people cheat their companies does not furnish an excuse for you nor exonerate you from cheating yours.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.