Hello Chiara
With SBB you cannot cancel international tickets online. After purchase, it is only possible at the travel center or by phone. Thus, the 30 minutes cancellation margin does not apply to international tickets.
You can try contacting SBB to see if they agree for a refund although Supersavers cannot be cancelled at all.
CH: 0848 44 66 88 (0.08 CHF / min)
Int.: +41 51 225 78 56
24/7, waiting times are possible.
Kind regards,
Roland