Apalling Customer Service

Rented a car from them, drove it no problem, handed it back at CTN airport and waited for them to check it, got told all was ok we can go. 4 days later got an email from a Mr Marlen Kallis claiming we had a dent on the rear door and was sent a claim form. I signed the claim form but made a note that we had no clue of any dent as nothing had happened to us with the car, and asked how can they 4 days later tell me my car had a dent after clearing it on arrival. I also informed them I took collission damage insurance dn we can claim from them. To date I have had no feed back of any sort, An my so called refundable deposit of R2,500 was never returned to me or not even an explanation about costs involved in a damage we had no clue about. Honestly this is to me appalling customer care service!!! Sent an email to the same Mr Marlen Kallis on the 27/02/2019 to date still no reply!! HELP PLEASE