Complaint Review: ENTERPRISE RENT A CAR

First let me start by saying I have rented from Enterprise a few times in the past with no real issues - this time was different.

My most recent experience started with a rental I needed while my Van which was recently in a hit & run accident was being repaired by the body shop located right next door to Enterprise.
My Insurance Company had made the arrangements with Enterprise to pick up the rental right after I dropped off my van. 

The sales associate & I at Enterprise started with the standard walk around inspection looking for any visible damage to the car which we both agreed looked pretty clean other than a few minor scrapes/dings - nothing major - so I agreed signed off on all the Insurance waivers offered - I had used my credit card (Visa) for the $50.00 hold required & knowing my Visa has Vehicle damage protection.

Upon the return of the car 3 days later when my Van was completed is where I ran into the problem.
The sales associate did his walk around inspection while I was inside - he then came in & said there was some damage to the car - we proceeded to walk out to the car to see the damage which he pointed out was on the underside of the rear bumper right by the exhaust cut out area- was a small crack about approx. 3/4" long - at that point I said this could have easily been overlooked by both of us on the pre-inspection - unless we were looking from a certain angle or distance you could not even see it because it was on the underside of the rear bumper.

He claimed no way this could have been overlooked & preceded to right up a damage report.
So trying to make a long story short Enterprise has filed a damage claim against me for prior damage I did not do.
I did return the following day to take photos of the damage myself, for the record which I did - they already had the car next door at the body shop & a repair bill of $689.20 which is a bit excessive. 

I have disputed the claim & have recently received a letter from there Damage recovery unit stating I need to notify my Insurance Co. or my Credit card Co to report the claim or If I want to pay for the damages myself they will send me a bill along with the supporting documents.