Go to the Georgia State Patrol website. Locate the Post closest to the area where you were stopped (that is likely where he works). There will be an address and a telephone number for that POST. Call the number and confirm that he works there. Then send a written complaint in to the POST commander.
Good luck to you. This sounds like an unfortunate situation. I would observe, however, that if your registration was expired he can lawfully have your vehicle towed as it is illegal to drive a motor vehicle with a suspended registration. With that said, it is pretty unusual for an officer to do so.
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