Well I got disconnected from my original webchat so here's where it gets picked up. :-
Peter :  Hi Jon, cheers
Jon:  Would you like me to check if Matt is available for you?
Peter :  don't mind, would just like a phone that works :-/
Jon:  I understand that you are having problems with your device rebooting and that you have performed a reset on the phone. Can you just confirm that this was a factory reset?
Peter :  Settings / About / Reset Your Phone
Jon:  Yes, that would be a factory reset. I am sorry but In that case I would recommend that you return the device to your retailer for an exchange. This is not a known fault so I would not anticipate that you would have any further issues with a replacement handset.
Peter :  not a known issue?? 
Windows Phone 8 users report random reboots and battery issues | The Verge
Peter :  
http://forums.windowscentral.com/htc-8x/200872-reboots.html
Peter :  
8X reboot survey - xda-developers
Jon:  I understand that there are reports of similar issues on the internet, but this is not a known issue.
Peter :  I purchased the device on the 2nd I thought there was a 14 day returns policy?
Jon:  That is dependent on your retailer. If your retailer is not able to exchange then we would need to book the device for repair.
Peter :  cheers for your time Jon, seems it was a waste of mine
so Apparently though it's been reported and people are calling them reporting this it's not a known problem :/