Did you use the Mobile Wi-Fi 4G router because of network problems? In that case you can return it free of charge once your Internet connection has been restored.
Put the router, the charger and the SIM card back into the original box and hand it in at a relay point near you. You have one month to return the Mobile Wi-Fi 4G-router.
Have you lost or thrown away the original packaging? Put the items of equipment and SIM card in a new box and stick the relay point label (which you will need to download and print) on it.