My company switched insurance companies last year after they'd been with the same company for 20+ years. I sent in a big claim at the end of last year, right before the switch-over. After a month and a half with no response, I reached out to find out what was going on. they claimed to have no record of my claim whatsoever, so made me resubmit from scratch.
A month later they post that the claim has been processed, and "discounts have been applied". When I went to check it out, "discounts" turned out to mean they had denied the claim entirely. So I emailed them, asking for an explanation.
They told me the treatment I received was not valid with the diagnosis code provided by the doctor. So I asked them for an explanation of what had changed in their policy, given I'd been submitting the same treatment under the same diagnosis code for multiple years with never a problem. They responded my claim was under review.
Now a week later, they just changed the claim status to "processed" again on their website (without notifying me, I've been checking daily). It appears they have still denied the entire claim... but can't tell for certain, as the language they use for everything is completely circumspect...