My Hotmail Plus account has changed to an ordinary Hotmail account with adverts etc.

I added a new email account to the Send to/Receive from area (successfully) and then found that my Hotmail Plus account had suddenly changed back to an ordinary Hotmail account with loads of annoying adverts!  How do I get my Hotmail Plus account that I pay for back?  My subscription is valid until next July.  Tried Billing Dept but they referred me to here.  I have NOT changed to Outlook although the page I used for the addition of the new email address did seem to be an Outlook page!