That right there should tell you they are not real debt collectors. Not sending that letter out is the first of their many offenses. Collectors in Michigan need to be licensed. That is why I included the link to the form for you to report them there as well. Did they give you any sort of company name?
I didn't figure they were, and I blocked all the numbers and reported them to the FCC, but it still is unwanted calls, you know? No, they were very evasive. I actually called them last night to see what the company name was when they answered, but there was no greeting, no options. Just immediate elevator music and 5 minutes later an automated voice proclaiming "Thanks for your call. A representative will be with you shortly."
The FCC does not have jurisdiction over debt collectors which is why I gave you those other links. The DNC does not include debt collectors. They have their own special law which i mentioned in my first reply to you.