What type of installation are you using? Is it a full-stack or native installation? I assume they should be both the same, but can you also get access to the console? If so, you could try to give the user superuser credentials via the command prompt:
Go to:
/edx/app/edxapp/edx-platform
Then:
sudo -u www-data /edx/bin/python.edxapp ./manage.py lms --settings aws shell
from django.contrib.auth.models import User
me = User.objects.get(username="user_name_of_the_user_you_want_to_be_super_user")
me.is_superuser = True
me.is_staff = True
me.save()
(Edit: forgot the command to get into the shell)