Nonsensical diagnosis code for my dad’s 2nd hip replacement- 14k bill. Help please

My dad had a hip replacement at the beginning of this year after his osteoporosis diagnosis in both hips. Shortly after his recovery he went ahead and did the next hip replacement.

First hip replacement insurance was all fine- he hit his out of pocket max and everything. Second hip replacement he all of a sudden gets hit with an over 14k dollar bill.

After digging into it and looking through his EOB and insurance claims, it seems the first one had the right diagnosis code of osteoporosis. The second one they billed it as EXTENDED OPIOID USE?!

To clarify he is one of those people that doesn’t like taking pain meds- he didn’t even finish his post op prescriptions. He is a non native English speaker so I always feel there might’ve been some misunderstanding somewhere but he most definitely did not have extended opioid use. Even if someone did, why would you have that be the diagnostic reason for a hip replacement. doesn’t even make sense.

We called the hospitals billing department over a month ago, they said they’ll submit it for code review. Now today we get another 14k bill so I’m guessing they didn’t change it?

We’re at a loss- this is absolutely nonsensical. What do we do?