11 km/h too much in Schweitz

Tach, I just got a love letter from the cantonal police Zuerich, I was driving too much on the motorway A1 a month ago 11 km/h (measured 117 -6 margin) and should therefore transfer 75 euros to an account of the post bank in Karlsruhe…. First: 11 km/h on the highway in the unfavorable area (no construction site, no accident, nothing.) ??? Second: 75 euros?? I think I spin. I know that elsewhere the penalties are higher than in Germany, but for 11 km/h on a carbah. I don’t see how much to pay. Therefore, my question: Can those who enforce it at all? Further, how can I deal with it? Third, what consequences do not pay if it is not issued? Thank you for all the useful answers, Dj