HTTPS Proxy Login

HI, When ever i'm connected to my work VPN through ATT Global Network Client I get a popup requesting me to enter my HTTPS Proxy Login details. I've tried all the usual password with no luck. Also contacted my work IT Dept who advise proxy is turned off and to contact Apple for further help as they dont support ICloud. Apple say to contact my work IT Dept.

Any one got a fix???

ICloud wont sync whilst i'm connected to ATT&T, however, It works when not connected......

thanks