Notes

We rent a car a few months ago in Phoenix, Arizona, and in order to get rid of any issue related to the car during our trip, we subscribed to an insurance offered by Sixt.
During our trip, on the last night, while we were having diner, another driver hit the rear bumper of our car. We first didn't notice it, since it was by night and we didn't use the trunk. However, we found a note on the windscreen. When we finally realized that someone had bumped into our car, we were on the way back to the airport and to Sixt cars drop-off. We immediately asked the Sixt employee what we had to do: he told us that, since we paid for insurance, we didn't have to do anything but filling the form to declare the issue. What we did, and we also add the name and references found on our windscreen that night. Back at home, a few weeks later, we received a mail and an email asking us to fill again forms regarding this incident. Although we already did it at the airport, we filled it again and sent it back to Sixt by mail, including the third party contact details.
That is for the context back 5 months ago.
Today, we are harassed by a claim agency. At least 2 mails, 3 emails, many phone calls and voicemail messages within 2 weeks. Worse than the frequency, the agency has been threatening us a couple of time as if we were thieves, even though we already answered the questions asked before. Sixt never reached to us before sending our file to this agency and they won't answer our emails now. That is unacceptable. This is the worse client treatment we’ve ever seen in our life. What kind of customer service could not even warn you that they will pursue damages via a claim agency, knowing that we did our best to be as helpful as we could and we were clearly not responsible for the damages?
We are requested to pay because we didn't go the police when the event occurred. How are you supposed to behave when an employee tells you clearly to fill a form and to go? It seems totally unfair. What is the point of buying your insurance if we are not covered especially when we were not responsible for the damage? Apparently, Sixt was not able to get the details about the person responsible so they’re trying to make us pay. We did contact the man who left a message on the car, he was a witness of the accident and he told us that it took Sixt many months to contact him to get his testimony. Do you think the best way to get details about an event and to reach the responsible is to wait as much as possible?
We already wasted a lot of time and energy on your requests so far. The question rising now is simple: what is the next step? We chose to rent at Sixt knowing it was not the cheapest deal because we trusted in your services and especially in your insurance.
Obviously that was not the best choice, and we learnt from it; even though we had good experiences with your company in the past, would never rent again to Sixt, neither in Europe nor in the USA. Also, needless to say we would not recommend your services to any of our friends or family. It's still unbelievable to see how corporate interest could totally waive customer satisfaction.