Even when you are in a forced-quarantine state, as long as the Wi-Fi is in your possession, you will be charged for an extension fee.
If you did not apply for an extension and the device is still not returned 3 days after your supposed return day, it will be deemed a lost device and you will be charged for a compensation fee.
If you are not able to return it within 3 days, please apply for an extension through your "Customer My Page" by 24:00 (midnight), one day after your supposed return day.
For details on applying for extension, refer to this page.