Seems the username and password saved in control panel isnt used by rasdial in command prompt. instead you need to put the user/pass into the command line:

C:\Windows\System32\rasdial.exe "VPN"...

it might be that i need to install some additional windows features now i upgraded to 10 but previously this rasdial command line worked for me to do this

C:\Windows\System32\rasdial.exe "VPNname"