I have an old Vodafone Fritzbox router that needs to be returned, as stated in an email I received. The provided return address is "Bielefelder Strasse 45, 33428 Marienfeld," but I am currently located in Berlin, Germany. I am unsure if it is necessary to return the router to Marienfeld or if I can return it to Berlin instead. Additionally, the email mentions that I should "frank the package sufficiently," and I am uncertain about the meaning of this instruction. It would be greatly appreciated if someone could provide assistance in understanding how I can return the device.