How can I restrict access to default azure website?

We are experiencing a Dodos attack (I guess) as we are receiving millions of HEAD request to our web site. We have secured it but unfortunately Azure has the default domain xyz.azurewebsite.com and the "attacker" is making request to that URL. Even if I add a network restriction the server still goes down as to produce the "403 forbidden" page I guess it uses some resource. Any Ideas to prevent this ?