It’s generally possible to appeal insurance company denials, but it requires patience, persistence, and your doctor’s support. I did it successfully to get VSL #3 DS covered, but it took nearly a year. I had to escalate my appeal to the state Insurance Administration, and even that took a few rounds. Eventually the insurance company caved, and paid all of the bills retroactively.
Generally the insurance company has an appeals process, and it usually has two levels (the second level is to reconsider the first level denial).
Is your doctor willing to invest the time to appeal?