Motion to dismiss? I received a ticket for invalid registration due to taking insurance off the vehicle while inoperable?

Recently, GA has implemented a law making it mandatory each registered car is insured. I paid the registration for my car. While I had it insured the car became inoperable, I took the insurance off of it and got insurance on another car. Less than a month later I figured out what was wrong w/ the 1st car and had it insured again. While I was driving the 1st car again, I got pulled over & ticketed for invalid registration. I went to the tag office & jus signed paper saying that it was inoperable during the time it was uninsured and they cleared it.However, when I went to court concerning the ticket of invalid registration they wanted $770 for invalid registration due to the tag office suspending my tag. The solicitor told me she would change the charge to unregistered vehicle $550. Fair?