What is the ruling on lying to an insurance company in order to get a car repaired, and how can one absolve oneself of this sin, given the inability to inform the company or return the money?

What you did, defrauding and lying to the insurance company, is not permissible. You must repent, seek forgiveness, and return what you took unjustly, for the Prophet, peace and blessings be upon him, said: "On the hand is what it took until it returns it." You must return the right to the company, even if through indirect means. Your need for the car or your fear of the case being taken to court does not make it permissible for you to lie and take money wrongfully.