Disputed damage charge after vehicle was returned

I rented a vehicle from Europcar at the Hartfield branch and the staff were helpful throughout the rental process, which I appreciate. The vehicle was inspected upon return and my deposit was refunded, confirming acceptance of the car in that condition. Afterward, I received an email claiming there was a dent on the roof that was not previously reported. I was later invoiced approximately R4,800 for this damage, which I dispute as it was not identified during the return inspection. I need clarification on this charge