Supplemental Insurance provider is fighting me at every turn

I have an accident policy through my employer. I live in TN.

I suffered a qualifying accident in April of this year. I’ve been diligent about submitting proof of doctor visits and what was done. They were easy to deal with when it came to the first two payouts, totaling just shy of $6000. They did drop the ball a little on the first payout, coding it as a non surgically repaired fracture, but this was remedied on the second payout.

Since then, I have had follow ups and PT, including application of a medical device in the form of a fiberglass cast. By my math, they still owe me just shy of $900. I have submitted the necessary documentation, but every time I call, I’m either told that it’s being reviewed or they say they’ll resubmit it to the claims team. I get no communication to know the status of my claim.

Do I have any type of case? What’s my recourse?