I am not liable for your damages

I rented a car from Avis. Through my insurer Outsurance. Upon returning the vehicle, the consultant checked the vehicle and then told me that he is happy with everything and I can leave. 30 minutes later he called me on my cell and told me I forgot my keys in the car and that he has something to show me.

Upon my return, 1 hour after I had dropped it, the car was moved from where I parked it. Only about 2 metres but moved nonetheless. He told me there is a dent in the car and that we are liable for the damage. I told him that we don't know what happened in the 1 hour that we were gone and that he told me he is happy when we left, so why are we supposed to be left liable.

I see the amount for damages was deducted from my credit card. I have an email where the consultant states he moved the car and that I was phoned back 1 hour after already leaving the premises. I signed a form there stating that I see the damages, but made a note on the form about everything. How can you keep me liable when we do not know what happened within that 1 hour that the car was out of our possession. The cae was no longer our responsibility the moment the consultant got in the car and moved it. I need my account to be refunded or I am taking this up with the ombudsman and small claims court.