I wouldn't worry about 'running afoul' of local laws. You have evidence there was no issues/damage when you returned the vehicle. A bad picture the day after is not any proof that you did anything, along with replies from their customer service stating there was no damage charge.
It seems to be an erroneous charge and the CC should be able to reverse it. I would also follow up with the France service site and tell them you were charged and show the credit card transaction again, despite being told there is no damage (provide copies of emails, documents etc). and that you will be disputing the charge if it is not reversed.