Simplest way: Use the customer selfcare portal and there the relocation service. You enter your new address and provide a scan of your deregistration letter showing that you moved out of Germany.
This should be enough to trigger the cancellation - but keep in mind that you have to pay for another three months after your relocation request has been received by Vodafone.
And please send back the rental devices in time to the Nuremberg address - this has to be done on your own expenses and on your own risk, so please -in your own favour- choose an insured and trackable service and keep the receipt that you sent the devices.
