Can anyone provide assistance with this?

I've had a damage claim from a popular hire car company from 6 months ago that amounts to £600. The dent is tiny and is almost not visible in the close up digital photo I have been sent.

I'm pretty sure I didnt do the damage as I only drove the car one way direct and then parked it up, no car parks or supermarkets where it is likely this damage was done.

The car on pickup had a lot of undeclared damage and I had to add this and sign the sheet, so it is likely that either I missed it at collection, or it was done after it was collected from me.

Many of my cars from this company (i travel a lot in hire cars - this is the first time of any issues in 5 years) are covered in damage but it is not marked on the damage sheet. It is like a lottery for the poor person taking the car to see if they can mark it all down without missing any tiny bits.

The dents are around 10mm long and there are 2 of them.

Many thanks in advance.