What state do you live in ?? Most states have a depratment of Professional regulation ( or someting like that) where they would have to obtain a license. This same department would also be able to tell you if they ae licensed or not.
If they are not licensed in your state (and are required to be), then they cannot legally collect. They will attempot to hoping you just panic and send the money . You can turn them in for engaging in collection activity without a license. This will create a small headache for them.
Eventually they will just pay the fine, get the required license and then collect on you legally.
Same applies to Attorneys, they need to be memebrs of the bar in your state(as well as their own) in order to collect. This information is a little harder to get, but still obtainable.