Trying to fill in CF83 but my account is an organisation not an individual

Hi. I'm trying to submit a CF83 before the April 5th deadline. However, after filling in my government gateway details I'm told: "Access denied. We are sorry, but this page is restricted. Organisations cannot access this form." The only reason I can think that I might be an organisation rather than an individual is because I was self employed very briefly many years ago. I told them at the time when I stopped being self employed but I still appear to have a business tax account. Do I need to re-inform them that I am no longer self-employed? Would this get my account re-instated as an individual account? Or might there be another reason I'm categorised as an organisation? If not, is the only way for me to complete the CF83 by submitting a postal version? And if so, what if it is not received by HMRC until after the deadline? Will the date I posted it count? (I live abroad and I'm worried that it may take some time to arrive). And how might I receive proof that it definitely arrived? (Post seems less reliable than online so I'd really like to complete it online if I can).

Hi riversandseas,
You may have created an organisation account when registering with SA. 
You will need an individual account to apply to pay Voluntary National Insurance Contributions. 
If you are struggling to set a new Gateway account up, please contact the Online Service Help Desk 
0300 200 3600 from the UK
+44 16 1930 8445 from abroad.
Alternatively, you can select no to applying online and fill in the form to then print and post and please submit this before the deadline. 
You can request a call back to discuss payment of voluntary NICs for tax years between 2006 and 2018 by completing and submitting an online form to register your interest.
This will be sent to DWP and a call back arranged within 8 weeks.
Request a call back to pay voluntary National Insurance contributions
Thank you.
 

Hello. I tried setting up a new Gateway account but after doing so it told me my personal tax account was still linked to the first Gateway account and could not be changed. So I am still not sure how to change myself from an organisation to an individual. Calling directly would be too expensive. But I have requested a call back through the online form. I'm not sure what happens if I miss the call. Our time zones are quite different so I might be asleep for example when a call comes. If I miss it can it be rescheduled in some way?

Hi riversandseas,
The Online Service Help Desk may be able to help with setting up a new account.  
Call the Online Service Help Desk on 0300 200 3600 from the UK or +44 161 930 8445 from outside the UK
You can use the webchat function ‘ask HMRC online
Technical support with HMRC online services
When DWP set up your call back they will arrange this for a suitable time, this could be as early as 8am your local time. 
Thank you.