Held liable for damages

My wife has rented a car from Avis before. When the car was returned, no inspection was done. Months later, she received an SMS from CreditWorx for an amount outstanding on the Avis account. According to Avis, the outstanding balance is for damages to the rental car. The "damages" were not caused by my wife, nor can it be shown that an inspection was done. Now, when she needs to rent a car from Avis again, there is a block on her account and Avis won't give her a car to rent.