If the matter is as you describe, then you have to tell the company the truth and not use tricks to take from the company that which it has not given permission for. If the rent of the house is 900 pounds, it is not permissible to write it as 1200, whether that includes the utility bills or not, because the company has differentiated between the two things and has allocated a specific limit for each.
It is no secret that honesty is one of the greatest of characteristics and it is the means of all goodness, as the Prophet (blessings and peace of Allah be upon him) said: “I enjoin you to be truthful, for truthfulness leads to righteousness and righteousness leads to Paradise. A man may continue to tell the truth and endeavour to be truthful until he is recorded with Allaah as a speaker of truth. And beware of lying, for lying leads to wickedness and wickedness leads to Hell. A man may continue to tell lies and endeavour to tell lies, until he is recorded with Allaah as a liar.”
Narrated by al-Bukhaari (5743)and Muslim (2607).
Recording the amounts as something other than what they really are involves lying and deceit, and using tricks in order to consume wealth unlawfully. All of that is haraam. Allah, may He be exalted, says (interpretation of the meaning): “O you who believe! Eat not up your property among yourselves unjustly” [an-Nisa’ 4:29]. And the Prophet (blessings and peace of Allah be upon him) said: “Whoever deceives us is not one of us.” Narrated by Muslim (101).
So you have to be honest and tell the truth about the situation; that is the way that leads to salvation, goodness and blessing.
If anyone has done that previously, he has to return the money that he took when he was not entitled to it, to the company. If he fears that this will cause him trouble, then he may send the money to the company by any means, and he does not have to tell the administration of the company what he did.
And Allah knows best.