<human>: Could you distill the essence of the text into 1-3 sentences?

Background: I have medical bills from an auto accident last July. I have insurance, but they have refused to pay two of the bills in the entirety. I have been going back and forth with them in particular over the ambulance bill. My coverage if for 100% emergency transportation, yet they refused to cover the last $400 of the bill. Needless to say, but I did not pay the ambulance company directly when they sent the bill to me. 

After being gone for the holidays, I come home yesterday to find a letter saying that this bill will go to collections if not paid. I do not want this to happen, so I called the ambulance company today expecting to settle the bill. But, unfortunately for me, they said that it was already sent to collections on 11/30. 

What should I do? Is it even possible that they sent it to collections on the weekend? (Being the Sunday after Thanksgiving seems a particularly dick move... but that's just me venting.) Should I call the collections agency ASAP to try and keep this from impacting my credit score? (maybe they haven't reported it yet?) I am a student, so $400 is a big deal, but the one thing I had going for me was a spotless credit report... oops.
<bot>: medical bill went to collections 11/30/2014. Can I pay it ASAP and avoid the ding to my credit?