Spurious cleaning charge in La Rochelle

On returning the car I was charged 60 euros for car cleaning. The only mess in the car was dry mud and grit in the footwells. No stains were on the upholstery or anywhere else in the car. The grit would have been cleared with 2 minutes vacuum cleaner. Unfortunately we were running late for our flight and were not in a position to take this further at the time.

Is it company policy to:-

* now charge for a car valet?
This is effectively a hidden cost over and above the original quote price which I'm not aware that your competitors also charge.

* not make it clear that this hidden charge will be applied on return.
The contract was stamped with a "max 80 euro charge for cleaning" after all signatures and initials had been made. Do you expect customers to read the contract after they have signed the policy?

* no charging structure for the car cleaning policy.
The maximum charge was 80 euros. So I fail to see how some dry mud / grit in the footwell is 60 euros. My car was then checked after my colleague. I was not charged as my wife indicated this charge was nonsense. The Alamo employee then indicated we should share the cost for my colleague. Where is the pricing structure in this?

Please indicate where on the policy we signed does it say dry mud in the footwell will be charged for?

Given the stamp was made to the policy after a signature, I believe this charge is illegal.