car allowance

Q: I am working in a company as an engineer and as per my designation car is allowed for my traveling but my company does not have a car infact they pay me money to hire a rent car for my visit. My question is that if I don't use a rent car and claim rent car bill, will it be halaal or haram. For example, I have to travel from city A to B. I travel it through train which is cheaper but to the company I claim rent for car because as per my designation car is allowed to me for my ease. But I want to save some money so I rather use some cheap transport method and claim rent for car. Kindly also note the this is the environment of my company. All my colleagues do this and if I don't do this, they will whisper against me to the higher management and I have a chance to lose job. Even if I travel by train or some other transport and want to tell this to my company then my colleagues will become angry with me and will speak against me. So kindly answer me keeping in mind my both scenarios. One is that as per my designation, car is allowed to me for my ease and second, the environment of my office.