Before you pay the amount of the second invoice sent you by the hospital, you need to speak with the accounts receivable department to make sure what amount is the correct amount before paying it. Carefully ask questions as to the reasons for the two different amounts and why there supposedly was an error in the billing resulting in the second invoice.You might consider asking the person who you are speaking with about paying the lesser amount as payment in full as opposed to the second invoice given the discrepancy. If agreeable, send the payments for the first payment with a note stating payment in full. Keep a copy of the note for future need. My concern is that the hospital may be inflating its charges with the second invoice.