Enterprise Rental Car Claimed damage after returned deposit Decatur, Georgia

I rented a car from Enterprise in Decatur, GA.  I did not take the insurance.  I returned the car and did the walk-around with the agent, who did not find any damage.  He signed off on the rental and refunded my deposit, which was refunded back to my debit card.  About two weeks later I received a letter from Enterprise claiming that I had done damage to the car and they wanted me to give them my insurance information so that they could claim the damage.  The letter did not even state how much the damage was.  I immediately sent an email to the email address on the letter.  I NEVER received a response, but I did receive several more letters.  Finally, I got a phone call AT WORK (they never tried my personal phone number first) months after I tried to resolve the matter, although they would not return my emails.  The representative said if I did not give her my credit card number or insurance information they would sent my name into a credit recovery agency.  Now, my question is this:  How can they claim damage AFTER they refunded my deposit.  By doing so, they confirmed that I had done no damage to the car.  Now I am getting phone calls from a credit recovery agency who is hounding me.  These charges are fraudulent and I am afraid they will leave negative information on my credit report.