Should answer threat letters from an insurance company if there charges weren't included in court restitution?

Your question is a bit unclear, but restitution in a criminal case and the ability of an insurer to seek reimbursement for money paid out in the same situation are two different things. They cannot "double recover" but it seems from your question that the amount they want was not included in the restittuion figure so it seems they would not double recover. Therefore you will have to deal with them and work it out, or they likely would sue you to recover it.