Actually, the most effective way to proceed would be to  file a lawsuit against the insurer for "breach of contract": for violating the insurnace policy's (which is a contract) obligation to pay in these circumstances. If you can prove in court that under the terms of the policy as applied to the facts, they should have paid, the court can order them to pay. If it's not worth the cost and effort of a lawsuit, then it's probably not worth pursuing; you could try filng the DOI complaint, which is free, but it it is unlikely that the complaint will result in being paid.