If your not under supervision this is a “knocking and talk” investigative tactic. House visits are not codified in law, make no mistake they are investigating you!!! If you cooperate you make their job easier and cheaper to conduct, which encourages these investigations. I NEVER answer the door and have my attorney follow up with whatever contact information is left behind. Once your attorney gets involved they cannot contact you directly. My lawyer don’t charge for this kind of follow up, but some may.