Is it permissible for me to continue using the fuel provided by the company for its car, knowing that it was acquired through unlawful means, and does the sin fall solely upon the company, given our adherence to "Ask not about things which, if made plain to you, may cause you trouble"?

The reason for the revelation of the noble verse: "O you who have believed, do not ask about things which, if made apparent to you, would trouble you" was due to mocking questions from some people. As for continuing to obtain gasoline from the company unlawfully, this is not permissible because you become a partner in sin. You must obtain legitimate gasoline or pay for it out of your own pocket. It is better to look for another job. You must also repent to Allah for what has passed and resolve not to return to such an act.