If I understand your story... The police pulled the vehicle over and instructed you to put your hands up and open the car door. Instead you stayed stooped down looking for your ring, creating a bona fide concern that you might be about to come out with a weapon. The police reacted accordingly. They claim you assaulted them and resisted arrest; you claim you did not and they assaulted you.
You need to be working with a criminal defense lawyer, and investigating whether any of the patrol vehicles had video and, if so, whether any of this was caught on tape. It's also possible that some of it was recorded in audio form. But you've waited a long time to get started with trying to preserve recordings, so get on it.

