"Sorry, we can't connect to your account. Please try again later." when attempting to activate access 2013 via proxy server

I am able to install Access 2013 but when it comes to activating it, it gives me the above error.

I have already had my SysAdmin add the following URLs to our whitelist but with no effect:

roaming.officeapps.live.com:443/
ols.officeapps.live.com:443/

Can anyone suggest anything else that I could try or any other URLs that I may need to add to our whitelist?

Many thanks,
Ricky