Thanks to Sixt's service, I was able to return the car smoothly. Due to road closures and traffic jams, and being in a rush to catch a train, I didn’t have time to refuel. However, Sixt proactively informed me that they wouldn’t charge double the fuel price. That said, Sixt's customer service hotline was impossible to get through. When I finally managed to connect, I was told they couldn’t speak English.