Hello Thuehajoill89
It is well possible that it concerns a case that happend last year while you resided in Switzerland. Usually, the dept collection process is initiated after a few months only.
You have to get in touch with the company in question, Intrum. Only they are able to provide you with the necesary documents. See their contact information in their letter. Even though you think, the invoice is not justified, you should take it serious if you do not want to get in troubles with the authorities.
SBB has handed over dept collection to Intrum, therefore, neither the SBB customer service nor we are able to provide help.
Kind regards,
Roland