Self Assessment for Trusts

I have registered my Trusts for Self Assessment as requested, but when I try to complete the required Self Assessment logging in using the Government Gateway ID that was issued when the Trusts were registerd, I get the message that I need to add a Tax to the Business Tax Account. However, when I go through the simple on line form, it tells me that: "There is a problem. This information does not exist for Self Assessment Online for Trusts, or it has already been used to request access to this tax or scheme." It tells me I should check my details or get HMRC Online Services help. I tried to call the Trusts Help line and after 6 minutes finally got an email to ask for help (it then hung up on me so I couldn't speak to a real person). However the email bounced. I don't know where to turn to next.

Hi,

You can contact our online services on 0300 200 3600.

Thank you