i used to be a medical biller so i do know the answer for you it is NOT your
responsibilty. The billing dept did not submitt to your insurance company on time for them to show time filing limit they have to look through there recorde you can not do this unless you are the one that submitted the bill.
call the medical billing dept in which u are getting the bill from tell them it is there job to find all the paper work to do an appeal with your insurance.Unfortunally for them it is way to late depending on the type of your insurance so they are going to have to write off the bill altogther. I would ask to speak to one of the main people in charge when u call the medical biller. i hope this helped you out