Domain missing after setup

How do I replace my missing Domain so that I can again set it to get my sales website working?

In the top right of: Home / List Addon Domains it now shows I have no Domain:   
Domains 0 / oo
Available / Contracted  0%

When I try to add that Domain back again, in the top right corner it brings up in red:
  Error..!
  Domain already exists
  Domains 0 / oo
  Available / Contracted  0%

This seems to have happened after having to change nameservers, just after setting it up.

Nobody knows your server. I would recommend you talk to the CWP support to fix problems on your server.