I think the letter needs the year mentioned, because Sixt has taken so long to get around to this. I ould also add that based upon OP's interaction with Sixt in 2018, he believed the matter was resolved in his favor.VoR61's letter is much clearer. I think you can be even briefer since the pickup info isn't really necessary:
"I am writing to you today because my efforts to resolve an issue with your claims department have been unsuccessful. Here are the details:
- On October ??, I returned a car in Milan with no damage.
- At the time of return, I asked your agent if she would like to jointly inspect the car's condition, but she declined.
- You have provided pictures of two surface scratches, but they are not time stamped and were taken at a different location from the return. I assume this damage occurred after the return while the car was in Sixt's possession.As the car was returned with no damage and you have produced no evidence to the contrary, I would very much appreciate this matter being dropped.Thank you for your time and consideration"