Online Services - Unable to submit SA

Hi. For info, this is not my first SA. But for the recent tax year, I completed my SA form yesterday, saving as I went along. When I tried to 'Submit' I get a message 'A problem occurred...' It recommends a) logging out and trying later or b) Selecting 'Next'. Logging out and in again makes no difference. Selecting 'Next' brings up 'You must complete the sections up to 4......' Which I had done but obviously there was an issue saving them. I'm not able to return to sections 1-4 to complete this missing info. I'm not able to edit the form. (The File a return menu options do not work). Exiting the 'File a return' and going back in, doesn't work. So I'm just going round in circles. I've tried contact the helpline but after going through the options I just hear that all agents are busy and the call ends. The digital agent just refers me to the helpline. Any advice/help much appreciated.

Hi,
For assistance you will need to contact HMRC direct: Self Assessment: general enquiries.
Thank you.