There is something else you could try.
1) Do a factory reset
2) Connect the kobo and choose the Computer setup option to get usb access to the kobo.
3) Use the "Registration Bypassing"
4) Do an manual update using "Direct Links to Kobo Touch Firmware"
This thread has links to explanations on how to do step 3-4.
https://www.mobileread.com/forums/sho...d.php?t=217160