What would a German do?

I got a weird problem with a neighbour, that demonstrates a typical German way of communication. My wife needed some room in a trunk of our car for shopping, so she removed a folding stroller from the trunk, and left it at our parking lot. (The parking place at our building's underground parking that belongs to us). In couple of hours Yulia came back, and did not find a stroller. She looked around and found it ~20 meters away, at some other neighbor's parking lot.

In the evening, I found a letter (with date, name and signature) under my car's wiper:

"Hi, I accidentally rolled over a stroller that was lying at your parking lot. Now I have some scratches on my car, if the stroller belongs to you, please call me +49NNN to discuss the compensation."

I wonder what I do next, obviously my German is not good enough to discuss these matters over phone, and Yulia would not stay calm during the conversation (though even if it turns out to be our fault, we still have an insurance for that).

I am also very curious, what would happen in US and Russia in the same circumstances?