Today, I got a note on my windshield from a neighbor. They claimed that I dinged their new car with my door the other day. I'm convinced it wasn't me. My doors swing open with zero resistance so I'm always extremely conscious about not dinging other people's cars. Even if I merely *tap* another car with my door, I always make sure it didn't ding and it never has, but I definitely would've left a note with my phone number if it did because I'd never damage someone's property without taking responsibility. They told me that I should consider the letter a "warning" and I'd better be careful or they would "come after my insurance." They claimed that they set up security cameras for both the apartment and the car after the incident, but I could not find any new security cameras on our building and I did not see any cars with dings in the parking lot tonight.
They did not leave their name or any contact information. They weren't even looking for money. The sole purpose of this letter was to scare me. But I can't help but worry that they're going to get revenge somehow. Like key my car, slash my tires, etc. Or even find some way to charge me with a hit and run, which is a misdemeanor. I know in my head that this sounds extreme and irrational but I feel very unsafe knowing that someone in my apartment building has a hunch against me and I don't know who they are and I can't resolve this issue personally in any way. 
Any insight on how I can put this situation behind me without reaching any resolution with this neighbor whatsoever? It would be one thing if I was able to talk to the neighbor and get some closure but the lack of talking to them face to face is driving my anxiety through the roof and making me think the worst case scenario will happen.