Hello Boitaumbau27
As you do not describe your issue, I am unable to help. And please, I am not personally liable. If you are unhappy with the offer, please reach out to the SBB Customer Service:
https://www.sbb.ch/en/help-and-contact/customer-service/praise-comments/claims-complaints.html
The SBB Community is run by volunteers helping travellers, so am I; thus we like a friendly conversation.
The cancellation process is clearly outlined in the GTC’s which you accept with every purchase. If you didn’t read them before purchase, no problem, but you cannot claim SBB for not having known.

You cannot cancel the STP 100% free of charge anyway. It has to be cancelled manually by a staff member. The administration fee is CHF 10, which is nothing compared to the ticket cost of the STP.
→ In the post you have linked, I made a wrong statement. The Swiss Half Fare Card does show up in the SBB Mobile App (provided you purchased it as a registered user), the Swiss Travel Pass does not (even not in the case it was purchased as a registered user).
→ The confusion among tourists between the SwissPass and the Swiss Travel Pass comes from the fact that the tourist pass was named Swiss Pass until 2014, and was then renamed to Swiss Travel Pass, while SwissPass became a resident product. Many travel websites and ticket agencies still talk about the Swiss Pass while they actually mean Swiss Travel Pass. However, being very active in the English-speaking community myself, I would say this is a big issue.
Kind regards,
Roland