I called to USTravelDocs Polish number and spoke to the customer representative. In short: they can't do anything, they just provide the same information that's available on their website, like robots. She just keeps saying the same thing over and over: you can either reschedule or transfer the case to another Embassy but we can't help you with anything on our side. BTW, I was able to reschedule the interview already using USTravelDocs website, just in case. It's not clear at all what happens if you just miss the interview, the customer service girl was unable to answer that simple question.