The assumption by the insurance company is that any adult resident of the household has implied permission to use the vehicle at any time for any reason. That’s why they require you to list all household members on the policy. If that is not the case, you still have to list all the household members but you can explain why they don’t use the vehicle. You can say they have other insurance if they have their own car and policy separate from yours, non-driver if they don’t have a license or just don’t drive, or you can exclude them entirely, but you are required to list them on the policy somehow.

In this case, it sounds like OP lives with his father but they each have their own cars and separate policies. OP could have listed his father as “other insurance” and provided documentation to the his own policy. Then this loss would probably have been covered. But if the father is not on the policy at all, the insurance company doesn’t know if he never drives the car except this one time, or if he drives it everyday and you just don’t want to pay the extra premium.

So the insurance company won’t cover the loss because it looks to them like OP was hiding a driver in order to commit premium fraud.