Someone Backed into my car..what to do?

So this morning I go out to my car and someone had backed into it. The mark appears to be from a hitch and hit midway up the middle of my trunk lid just above taillight height. My trunk will not close now and besides for that the car has no other damage to the bumpers or anything of the sort. I was wondering which deductible covered this since I have no idea who hit me. And if it would be replaced for free?