I'm a legal secretary/paralegal in the State of California (28 years experience). If you claim that you never received any legal papers, you have the right to a hearing on this issue.. It is called a "traverse hearing." At the traverse hearing, you will have to prove that legal papers were improperly served upon you. A process server, who is hired by the opposing party to serve the papers, may testify that s/he personally delivered said papers. Also, if you wish, prior to the court date, you can go to the clerk's office at the courthouse and ask to see the court file. The file should include an affidavit stating when and how the papers were delivered - this may be of use to you at the time of hearing, such as the date for which they claim personal or sub service took place, perhaps you were not home/possibly out of town..thus, you will have further proof. Bring all documentation that you have in your possesion concerning this incident.
Also, please note that once established that service was uneffectuated, it is possible that you will be properly served at the time of hearing, should the attorney wish to proceed with the case, being that this is is a collection matter. Since you co- signed, you are legally responsible. Colection cases are handled by way of filing suit and serving - and if no response, a judgment is then entered by the clerk or by the court. Judgments can be renewed every 10 years..it may, of course, vary in your State.
Please also note that when a lien for Garnishment of Wages is processed, it is always served and directed personally to the payroll department or any such person in charge of the company and its employees. It is never personally served upon the employee.
Should you have any further questions, please do not hesitate to ask.
My very best to you.
Peace, Love & Happiness,
The Mystic Wave