So sorry. It was a bad business move by your father not to insure you. At most he could take you to small claims court if you refuse to pay (just like any other uninsured employee). Although what about your personal car insurance? Would it cover you/him? It would probably in the end raise the rates though.
Like others have said, if he is giving you other support, that might go away. and who knows about a personal relationship? I am sorry that he is being harsh over a combined mistake. Maybe ask if he would split the cost since you both could be considered liable?
If you wanted to be retaliatory -- you could always anonymously notify the agent/insurance carrier that he has non-insured employees driving company vehicles.

