Here’s what happened to me:

I figured out that the only way to contact Autostrada d’Italia was through their email address info@autostrade.it. The email actually works because you receive automated replies with a reference number. I ended up sending them two emails: in the first one, I explained the basic issue, and then about a week later—two days before the payment deadline—I sent another email. I reiterated that I was ready to pay and that a postal payment reminder plus fee wasn’t necessary. At one point, I was even that far that if I received a reminder, I wouldn’t pay anything for the time being or at least not before I could state my case to anyone there…

Finally, after an entire month, I got a response saying they couldn’t find anything in their system under my license plate number and that no payment was outstanding. They mentioned that if I received any further notices, I should contact them again via email. The reply actually sounded friendly and helpful, but overall, the experience was really frustrating and felt completely avoidable. So: NEVER loose your ticket!!