Some idiot left a note on my door with this number, claiming to be "Daniel" and agent of some kind. The names on the paper are people we don't know. It was pretty threatening, basically accusing me (or them?) of a crime regarding concealment of collateral. I'm guess he was some kind of repo guy? It referenced a vehicle I don't have, nor have ever had. No business name, last name. nothing else, just a first name and a cell phone number.Doesn't seem very professional. My neighbor said he saw some guy looking in my windows and even tried to open my back gate and lift my garage door.

Call the police and let them know. That sounds more like a burglar trying to see if you're home

The first thing I would have done was filed a police report using the card and the neighbor's statement as evidence that he was trying to rob you.  I would also have made a copy of that card, and filed a report with the proper agencies as well as consulted an attorney to file an FDCPA lawsuit against that crook.

Read up on your rights here, get template letters to send and also make a complaint at this government site: http://www.consumerfinance.gov/

Also file a complaint with your State Attorney General's office.
List of State AG’s offices:  http://consumerfraudreporting.org/stateattorneygenerallist.php

I received a letter just like your explaining, with the name Daniel on it. I have a lock on my brick bar gate. So he couldn't get inn. He left it on my gate . I called it had a standard answering machine thru phone co. This letter is fake. They stole my Idenity 2 yrs ago got 2 cars in my name less than 30 days apart . I left a message to take me too court please so I can prove I never got a car from anyone.. God be with them if I catch someone in my yard . I'm making a police report tomorrow, and calling the credit bureaus.