Ok, here is where we are:

The head of Radisson Scandinavia took the time for an almost 1-hour phone call, pressed all the right buttons and apologized. Very good impression.

The CEO of Rezidor Worldwide apologized in writing and sent a voucher for a 2-nights-free stay. Good or not?

The opinion on the Radisson Spitsbergen waiter and on the GM's email was shared. As it turns out they do not have as much influence on the hotel owner (Hurtigruten), as they would like. E.g. they can not sack staff. Only Hurtigruten can do that.

Hurtigrotten has not replied to three emails.