Complaint Review: Enterprise RAC

We rented a vehicle on 6/25 @ 7:30am after all-night flight. First, the weekly rental charge as quoted was not honored. Finally quote was revised with added drop charge ( which we agreed to) plus charge for tank of deisel upon return ( elected as dropping off @ 5:45am ). Total anticipated/agreed charges were to be $508 plus charge for tank of fuel. The vehicle was returned @ 5:45am on 6/30 @ Enterprise lot in Edinburgh ( thus drop charge ) and keys put in drop box ( as lot unattended). Vehicle was undamaged during our rental (parked off street in Gullane except two short trips and return to Edinburgh and used less than 1/4 tank ). We also took photos of front, back and sides upon parking in lot @ Edinburgh Airport. Upon return I discovered my visa acct. had been charged over $1800. I contacted Enterprise International and later received an e-mail that I had been charged a 750 Pound Sterling "excess damage " charge due to damage to front bumper - cost TBD. I protested and sent photos. Last weekend I was given a credit of $745 resulting in net charges of over $1,050. No itemization or further explanation to date. I strongly suspect that I am not the first victim of such an unscrupulous organization. I do not intend to accept the charges for "damage to bumper" which we absolutely did not incur.