Have you tried getting the kobo OS flashed with an SD card at chapters/Indigo (you don't say where you are located). I've read on the "getsatisfaction/kobo" website that users were able to correct problems with frozen readers by doing that.
Or have you tried posting your problem on this site (
https://getsatisfaction.com/kobo/topics/) along with a ticket number obtained here (
https://kobo.zendesk.com/mobile/home)?
It appears that might be more effective than calling....