Headphones Missing

Myself and friend rented a car from Europcar at Atocha station in Madrid. When we delivered the car back I accidentally left my headphones on the floor of the back passenger seat. I contacted the contact centre who indicated that I would need to call the branch directly, they however do not answer on the direct line provided. I went to the station and they indicated that they do not know where the Headphones are. Eventually they took my phone number and I asked them for an alternative direct line in case the headphones are found. Once again the telephone number is unattended and no one answers and they have not called me. They also indicated that the car has subsequently been rented. I am absolutely certain that I left my Headphones in the vehicle. In reality, the fact that the headphones were either ****** or cannot be found is unacceptable from Europcar, given their reputation and global presence. Moreover, the lack of customer service and unattended phone lines have made this process extremely difficult and I am extremely dissatisfied.