One standard piece of advice given many times is to reach out to Kobo. Don't open your device to replace the SD card until you have dealt with Kobo support. In numerous cases they HAVE replaced bricked WiFi's by newer models.
As to how to reach Kobo, see what options are available for YOUR country.
http://kobo.frontlinesvc.com/app/lanpag might help.
Twitter DOES seem to be one route where many have had assistance. See
https://twitter.com/KoboHelp