Bills received at my place of employment

I live in New York State and recently received a medical bill at my place of employment. The name on the outside of the envelope was the doctors name and billing address and my name. The first bill I received had my name, place of employment and the medical services provided for me. The second bill I received just said anesthesia services, balance forward and did not specify the procedure. Even though it was addressed to me, it was opened by the mail department because that is the company procedure. The mail room is not suppose to "review" my mail but they do normally discard the envelope or staple to the correspondence. I think this is a billing company but I am unsure, therefore would like to know my course of action, if any. What are the rules if it goes too or is a collection agency? Can they lawfully send me correspondence at work? The mail is left on my desk.