gillan--
you said that this debt went into collections 5 years ago. sol in your state is 6 years, that means that the debt collector has 6 years from date of last payment to sue you. After that, the SOL is expired and they can no longer legally take you to court to collect. when was the last payment made on this debt?
Also, check your county court clerk's office ASAP, to find out if they sued you already. A lot of CA's sue people using an old address, or even knowingly using a wrong address, that way, they can sue you and get a default judgment because you never get served, so you dont show up at court because you dont even know about the lawsuit against you. This is illegal, but fairly common today. if you find that you were sued, you should immediately send a certified letter to the court where the lawsuit was filed, requesting that they vacate the judgment due to improper service. The law requires them to serve the summons on you so that you can take advantage of your right to due process. If there was no lawsuit, then something's fishy because the marshals only collect after a civil suit has taken place.
something else to consider--you said that the name on the paper you got was Ronald Moses. This name is on the list of current NYC marshals, so apparently the guy is legit. its time to check those court clerk's offices, to see when you were sued and what happened.