My wife had a baby in January 2018. We paid off the hospital charges for my daughter in February 2018 and for herself in June 2018, all on time.

Last week we received two bills from the hospital, one for each of them. For my wife, it’s a new bill of about $1200, exactly equalling our personal payments after subtracting insurance payments from the total charge. For my daughter, it’s about $300, but a slightly different amount than what we exactly paid. The reason cited is “Insurance Contractual Adjustment.”

If you actually subtract all the individual payments from insurance and my family from the total charge, they still go to $0 for both my daughter and my wife, so I can’t even figure out where they’re getting their numbers from. Is it even legal for them to charge us over a year after the fact? If they did this last year, we could have just claimed we hit our out-of-pocket max, but this year we’re not close to it. Any chance we can still claim it as a bill for last year and use it against that max instead of this year?

I know these are pretty specific, technical questions, but being in grad school, money is tight and a $1500 charge out of the blue has us reeling, so any advice would be appreciated.