I'm kinda confused as to what you are asking. Yes, collection agencies have to be registered with the state of Illinois in order to collect in Illinois. I don't think this means a law firm that represents collection agencies would need to be registered to do so. But if you are being pursued by a collection agency that isn't registered in Illinois, I would recommend contacting the local Attorney General's Office. Additionally, your questions are going to require more facts to answer your questions. If you think all of this is going on, it would be a really good idea to consult a local consumer law attorney to review your case and give you an idea of your chance of success and options. FDCPA provides for attorney's fees, so don't let lack of money prevent you from consulting an attorney.
I am not sure what you are asking, either, but if you want to know the answer, you should contact a consumer lawyer in your state. The NACA lawyer database is an excellent place to start. As a NACA member, I know there are excellent consumer lawyers in Chicago, so you are in luck.