Enterprise Rent-A-Car

I was in a car accident that wasn't my fault and the other driver's insurance paid for a rental car from Enterprise. When I got a call that my car was repaired I returned the rental car within 12 hours. However, Enterprise Rent-A-Car has terrible record keeping and they claim the car was returned two days late even though the repair shop has informed them that the car was returned promptly. So Enterprise claimed I owe them money for an overdue rental car. I talked with them multiple times on the phone and sent them letters showing why I do not own them anything and sending them documentation. On September 1, 2015 I spent almost an hour in their local office resolving the issue and they agreed I do not owe them anything. I even have a signed hand written letter stating that I do not owe anything. Yet I continue to receive bills and threatening letters from the company and local branch. The latest letter they sent me claims that I have made "little or no effort to clear [my] account" even though it took me hours to clear the account, when there should have been no account to clear in the first place. Their latest letter threatens me with a collection agency, small claims court, and reporting on my permanent credit report. All these continual threats and attempts to get me to pay come after I already have a letter from their branch assistant manager stating I don't owe anything. A word of warning! Don't ever do business with this company! They will harass and threaten you even when you owe them absolutely nothing.