Wait and submit the letter to collections when they contact you. I had an issue with Univeristy of Louisville Sleep center in reference to my daughter and they waited until 2009 (her bills/visits were from 2005) to send me to collections AFTER sending me a check for everything I had paid into them. I was livid because not only had I paid them but so had the insurance company 3 different times on the same claim (kept claiming they had not received and the insurance company electronically sent it where they said to which was wrong place so insurance sent a check on 3rd pay) and had proof the check was cashed. It was so much easier dealing with the collections on it because I just sent them the copies of everything and they got the matter fixed.
I hope your little one is doing better now.
I hope your little one is doing better now.