score:10
As the standard answer states, Super Sparpreis tickets are neither refundable nor changeable. This includes the travellers name. If you're lucky, you might get a refund out of goodwill. I wouldn't count on it.
Basically your son would be dodging the fare, which would at least cost 60 €. Again, some conductors may act on goodwill if explained the issue. Again, I wouldn't count on it. On the other hand if your son has your surname, the fauxpas might go unnoticed.
Since the new ticket would come cheaper than 60 €, I suggest you buy a new one - this time for the correct name.
ps: Tickets for children are 50 % cheaper, and 90 € for a Super Sparpreis are rather much, I think. Make sure you choose the correct traveling person category.
Upvote:16
I'm not sure what you wrote the first time, but I'd recommend writing to Deutsche Bahn a time or two again. You might get someone more interested in preserving customer goodwill over an honest mistake rather than mindlessly following the rules.
Make the following points:
Above all, be polite. Remember that technically you are in the wrong and Deutsche Bahn is in the right. You made a mistake. They didn't. So be very apologetic while explaining the situation, acknowledge that you messed up, and ask if they would be kind enough to help you rectify your mistake.
None of the above is a guarantee, but it will improve your chances.