Don't sign forms unless they are completed!! Beware AVIS

Having returned my rent car in Cape Town airport in good order on Sunday 29th I was told by the receiving agent that there was damage at the drivers door handle which I could not see. She said that if I compared it to the passenger door I could see it but couldn't. More is the point I am an extremely careful driver and couldn't see how the door could be dented without a clear sign of impact. She said write that you deny the damage on "the form and sign it" but although I did do this clearly the rest of the form was not filled in prior to my signature. I have not seen the final form. I tried to get my statement from AVIS still nothing and there remains a lien on my bank account. This is pure harassments as I always ask for FULLY COMPREHENSIVE insurance so I can hand the keys in and say goodbye. This is not the first time. I took pictures of the tyres, windscreen and other parts of the car where there was damage but not the drivers door because it wasn't damaged AS FAR AS I COULD SEE. Be careful when signing off the acceptance especially for white cars.