I would do some research on the internet.

https://www.beobachter.ch/konsum/kon...mahnt-grundlos

https://www.konsumentenschutz.ch/for...istungskosten/

First try to validate if it could have been you.
Then check what's the fine for less than 10 km/h over the limit. Even 111 CHF seems massive to me.

Then tell them you need the original fine and you only intend to pay as much as the fine was. Then pay the original amount and be done with it.

Just got a regular (non-registered) letter from a Swiss debt-collection agency, claiming more than 400 EUR for a minor traffic offence Italian ticket of 112 EUR from 2018.

I have no idea how they came up with this total (and why in euros?!), as no details were provided.

I am willing to pay the ticket + legally allowed interest (5%), but was firstly planning to request a copy of their power of attorney, then an itemized bill etc.

Giving it a second thought, I am wondering if I should pay any attention to a non-registered letter or completely ignore it?

Moreover, it is signed (illegibly), but there is no name under the signature, though the company header is present on the template.

What do you think?

First reaction is that it sounds dodgy but is it plausible? Were you there at the time of the fine?

If there's a number on the letter give them a call and google around to see if anyone else has had a similar experience.

I was there, and there is photo of my car, as well as the original fine enclosed in the letter
This is not the issue, as I do not plan to contest the fine, however I am not willing to pay for the exorbitant (and illegal) additional fees, which have boosted the ticket to more than 400 EUR.

My dilemma is whether to respond to this non-registered letter at all?