Frame And Members problems of the 2007 Toyota Matrix

I drive a 2007 Toyota Matrix. While driving down the road, something came loose and a loud rattle/banging was present. I drove to the nearest Toyota dealership and left it there overnight. The gas tank strap was broken thus causing the fuel tank to hang down. The dealership alleges that I must've hit something for this to occur. I am the sole driver of this vehicle and I did not hit anything with this car. Toyota would not cover this repair under warranty. I paid to have the part replaced. The dealership kept the old part.