Are they for real?

[bkarial39]

What is the name of your state? Ca
I recently received (at my place of employment) a letter, not certified just regular mail informing me that I was being sued for a hospital bill from 2003. At the time the charges came about I had recently hired on at the hospital but after only less than a month was hurt at work and ended up hurt and on Workmans Comp, (whew, not fun,) but got sick and needed hospitalization totally unrelated though. Now when the MD told me I needed to be in the hospital I told him I couldn't as I had no insurance yet,, he told me sometimes the hospital works with employees and not to worry about it. I believe I received one statement from them showing charges but no bill, nothing no other contact whatsoever. And being that I almost lost everything I had while out on a work injury I didn't pursue the issue to see if it had infact been taken care of. And since workmans comp pays so little I was forced to change jobs as this one would n't let me back until I had a medical release. So to make this novel shorter, here it is two years later, the people who say they are having me sued for the hospital has never even contacted me, and can they legally count the regular mail letter as an actual legal service of impending action? It does have court clerk signitures but thats about it doesn't really even give me a date to respond other than 30 days from the date I receive the letter, (how do they know I even got it) Just curious, and thanks for you help