"No COB on file" but we don’t have other insurance?

Does anyone have experience with this? My husband is on my health insurance plan and has been since we got married a couple of years ago. He does not have coverage from anywhere else. There were no issues with anything before this year.

Earlier this year, he had 4 pre-authorized infusions. Insurance covered absolutely nothing because of this lack of coordination of benefits. I didn’t realize that was even a thing if you had no other coverage. They haven’t covered any of his weekly labs or clinic visits or anything. I had thought that things were being covered because I would occasionally check his balance and find that he only owed a little here and there (which I would pay with our HSA and move on with my life). As it turns out, whenever we had a low or zero balance, the reason was not because of insurance but because the medical bills were being WRITTEN OFF by financial assistance. This happened with 2/4 of the infusions (over 40k). One hasn’t even billed to us at all (I can’t find a bill with that date of service in his my chart. I also can’t find an EOB or even a claim for that date). One of them was not written off, but I did see the bill for it and put it on a payment plan (20k). Our out of pocket max is 14k, and it was all pre-authorized, so I don’t think we should owe THAT much money. I’m beyond confused about all this. (Plus, I’m sure the infusion that was never billed will be billed eventually…).

I don’t know if I’m asking for advice or just venting. Sorry for this rant. I talked to the financial aid lady at the hospital and asked her what a lack of COB means, and she just said, “That means it’s not covered.” Gee, thanks, lady. My husband called the insurance people, and they were telling him it was because he had other insurance, which makes no sense because he isn’t paying for any other insurance plan. His premiums come out of my check every two weeks, and everything was pre-authorized. I work for this health system and am NOT impressed.