Hello Trixie,
If you have buy your ticket online, you have to call today our Ticketshop at this number: 0848 030 030 or you can write an e-mail with your booking number at: ticketshop@sbb.ch. At the station, you can buy a new ticket but they can’t reimburse the online ticket.
If you need more help, I advise you to contact our RailService (open 24H/24): 0900 300 300 (1.19/min.)
Kinds Regards,
CharlineB