You can also request a callback in this way:
https://www.swisscom.ch/de/privatkunden/hilfe/kontakt.html
Or you can report the problem via the chat bot SAM, which will probably not understand you and then hand the chat over to a support employee.
Or you fill out the contact form, where you can also upload a screenshot of the error message, then you don’t have to explain much:
P.S.:
Swisscom employees also read here, but it is not the official channel for fault reports.