Enterprise rent-a-car Blamed for damage we didn't do Longmont, Colorado

We rented the SUV for our 1 week vacation through the rocky mountains of Colorado and Wyoming. Half way through the week a loud whine began at high speeds coming from the steering column. We called the Longmont branch to get instructions on what to do and were told no help could be given, did we have a phone with internet, and we should call around to the nearest branch in Wyoming and see if we could find a replacement. 

After reaching our motel in Rock Springs WY we called the Enterprise 800 number and reported the issue with the car. The nice lady told us to go to the branch in Rock Springs Wy. We traded the car and set out on our way to Yellowstone.  We quickly returned to the branch because the tank was empty and the car we had turned in had a 3/4 tank full. We were told the difference would be made up when we returned the car. The two women from the Rock Springs branch jumped in the rental car and took off down the road. 

4 days later when we turned in the replacement car in Longmont we were told the original car had damage to the undercarriage and muffler and we obviously had taken it off-road and  we needed to pay them for the damage. We let them know we did not take the car off road. Either the damage had been undetected before we rented it or someone else did it after we returned it to the Wy branch for an issue coming from the front of the car.

The branch manager will not return calls. Received letter from ERAC damage recovery unit asking for our insurance information. Brother-in-Law works in the Colorado state attorney's office. Will ask them to investigate these practices. Not paying them a cent for damage we did not do.