They can "send you to collections", but you are doing the right thing. Keep sending the money and keep records. Find out if your insurance paid them, or if they were paid by Medicare. If that happened, you may not owe them anything but your deductible! Why? If the hospital had a contract with an insurer, or was paid by Medicare, they have to accept what insurance or medicare pays them. They can't charge you on an inflated bill already reduced by Medicare or an insurance contract. If you start asking them that, and contact your insurer or Medicare, you might put an end to this problem. Of course, if you had not insurance or Medicare, just keep working on the balance and don't worry: if they sue you, you can tell it to the judge who will give you payment arrangements.