What can I do if a different car has the same license plate number as mine, and is getting tickets sent to us?

We own a Jeep, and last month, a car with the same license plate number (a Chevy) got a parking ticket. The city of Maywood sent it to us, saying the vehicle was registered to us. We don't own a Chevy, and the ticket was written while we were 50 miles away. If they actually ran the plate, shouldn't they have seen that it wasn't registered to a Chevy? How can we prove that it wasn't us? It wasn't caught by a camera, just written out by a police officer. We don't mind paying the $30 if we have to, but we can't afford to have someone else racking up fees and ruining our driving records. Thanks