Unsuccessful Corporation Tax Submission

Hi, I tried to submit my corporation tax via an accountancy software and it said that HMRC rejected this. I then tried to do it manually via the online Gateway account with HMRC and it said I am not registered for corporation tax, which is odd as I have submitted returns before successfully. The deadline is approaching soon for submission and I have tried everything. I have requested a registration access code for corporation tax. I have also submitted my end of year accounts successfully. Is there anything else I can do to try and meet the deadline?

Hi,
We are sorry to hear you are having issues filing online.
Unfortunately we do not have access to your records on this forum.
For assistance you would need to contact the online helpdesk: Technical support with HMRC online services
Thank you.