You report a crime by going to the police and letting them know you'd like the state to press charges. The difficulty is that you've already spoken to the State Attorney who has told you to get a lawyer. That likely means they see this as a civil matter and believe it belongs in civil court.
Obviously, it's cheaper for you to have the state prosecute than it is to have to pay a lawyer, but the burden of proof is more favorable to you in civil court than it is to the prosecutor in criminal court. And because husbands and wives sign each other's signature regularly, with actual or implicit permission, even though your situation makes out fraud and forgery, a criminal jury may not find guilt beyond a reasonable when the defendant is a former spouse.
If the police and prosecutor won't go forward with this, there is no appeal procedure. A prosecutor has complete discretion to decide for himself what cases to take on and which to turn aside. Nobody, not even the President of the US can compel a prosecutor to charge a defendant if the prosecutor does not wish to do so.
So all that you can do is to report the crime to the police and see what they tell you. If the police tell you it's a civil matter, you can go over their heads to the state attorney and report the crime there and see if you can change the prosecutor's mind. If he's unwilling, however, you would have to hire a civil lawyer and sue your ex and the insurance company for the fraud.