Green Motion's False Damage Claim On My Deposit

I rented a car from the Green Motion Stansted location. During the pickup, the staff pressured me to upgrade the insurance to full coverage. I proceeded with the standard insurance package. On the drop-off day, they inspected the car and spotted a very minor (nearly invisible) scratch on the bottom of the windscreen, charging me the full deposit amount of 1,400 GBP. It was unbelievable. I only drove 200 miles for four days, and such an incident had never happened before. I denied the claim and did not sign the paper, and they became very angry with me. They even refused to provide a shuttle bus voucher, which was part of the deal. I am trying to get my deposit amount back, and I hope I will. I want to warn everybody about this kind of ill attitude from the Green Motion car rental company.