You should definitely inquire about the cost breakdown and then calmly and politely ask about resolving the unnecessary charge that was a result of the midwife’s error. As medical errors go, this is a very simple one with an easy resolution (they submit a revised claim to Oscar, then you get your new lower portion bill). If the first person you spoke to can’t resolve this, ask to be transferred to someone else.
(It’s my opinion that TONS of medical bills are wrong on purpose and since they are usually small, confusing, and sent to people who are either recovering from a medical issue or older and more easily confused, the bills are paid without any questions. That’s obviously not the case here, but the lesson to check on anything you have questions about is still a good one.)