Originally Posted by
perthite
The different reservation number may well have been a sign that you had been misidentified at check-in....
Could the OP have a common last name?
It's fine here for folks to say that OP should refuse to pay and get the local police involved, but this is scary in a foreign country where the opposite side might have ties to the police or at least are from the same culture and speak the same language. Plus, we should assume that OP had a plane or train to catch; missing a flight while one wastes an hour arguing with the police could cost far more than 420 Euros with no hope of getting it back.
Situations like this are reasons why I think hotels should be required to put a hard copy of the bill under the door during the night before checkout.