Health insurance is delaying my claim. I got a letter requesting a "Claims and Eligibility Review". What should I do?

In a letter, they’d like to review my medical history from a few years ago, and would like me to authorize access. They place this caveat: “under no obligation to sign this form and that we may not condition payment health plan enrollment or benefits eligibility on my decision to sign this authorization, unless this authorization is being sought for determinations of health plan enrollment, eligibility, underwriting, or risk rating.”