Short version:

DB train station staff sold me the wrong ticket - a second class ticket from Rome to Munich. I didn't have time to fix the problem before leaving on my trip to Italy. I'm taking the train back to Germany in two days and need a first class ticket from Rome to Munich. I have been unsuccessful at getting the train station personnel in Italy to help, nor have the DB internet or phone service personnel been able to help.

Is it possible to pay the difference between a second class ticket and a first class ticket on board the City Night Line train? My reservation w/ appropriate Zuschlag has already been booked & paid for.

Long version:

I bought a CNL train ticket with a reservation for a deluxe double sleeper accommodation last week, in Kaiserslautern. Travel date is this Sunday (2 days from now).

I had wanted to buy a deluxe single but by the time I got to the station (bahn.com wouldn't book my particular itinerary online), only a shared compartment was available. It's still a deluxe double, though, which requires a first class ticket.

At the station, the woman selling me the ticket insisted that I needed a second class ticket since I had to share a room. This got to the point that she called her colleague over who also insisted I didn't need a first class ticket. I should have brought up the CNL page on my phone right then to show her that I really did need a first class ticket but didn't think that quickly. Therefore, I got a second class ticket.

I am now in Rome, getting ready to go back to Germany in two days. I went to the station here and the not-so-helpful woman at the information desk told me "your train only has second class seats, so you only need a second class ticket". Also wrong.

I wrote to the Deutsche Bahn Italian help desk. They wrote back and said that while I needed a first class ticket, they couldn't help since I had purchased the ticket online. Well, I didn't purchase the ticket online but I don't have time to argue with them.

I called the Deutsche Bahn help desk from my mobile. They said I needed a first class ticket but weren't sure how I could get one from them, and put me on hold to speak to someone at their international desk. After 20 minutes it was getting expensive so I hung up.

I finally had the idea to call the Deutsche Bahn UK number and got another person who said I definitely needed a first class ticket, all I would need to pay is the "aufpreis", i.e. the difference between the two fares, but that she couldn't help me because there is no way the ticket would get to me in time. She said that I PROBABLY could pay an aufpreis to the conductor on the CNL train, but that she wasn't sure.

Does anyone have any experience with this? I expect to have to pay extra...I just don't want to get kicked off or be refused entry to the train.