First, move to a safe spot and check everyone for injuries. Call 911...

https://dlf-ne.org/what-if-the-other-driver-changes-their-story-later-a-paralegals-guide-to-protecting-your-claim/

First, move to a safe spot and check everyone for injuries. Call 911 immediately to get an official police report. Take clear photos of the damage and collect contact information from any witnesses