If your policy is a group policy, then it is probably regulated by ERISA. If so, you are entitled to a complete copy of the claim file by writing to the company and asking for all relevant documents that make up your file. They have 30 days to give it to you. When you get it, make sure that it contains at least the following:
1. your plan or policy
2. any summary plan description
3. any records you sent them
4. any records your doctor sent them
5. any records they received from authorizations you signed
6. any internal notes they made while processing your claim
7. reports from any doctors that they had look at your case.
Remember, if you are going to appeal your case, you generally have 180 days from the date you received your denial letter to appeal.