Amending a 2022 return and Claim for repayment of tax deducted (R40)

I wrote to HMRC last year as I belatedly realised I'd failed to declare income from a discretionary trust on my 2021-22 return. I never had a reply. However, this income was already taxed at 45% as it came from a discretionary trust. In spite of speaking today with both the Trusts department and the Self Assessment team and being on the phone for over 3hrs no one could help or update on why my letter has not been responded to. A search of your website would suggest I need to amend my 2021-22 SA return to include an SA107 with the trust income and that I should also submit an R40 to claim repayment for tax deducted. However, the advice also suggests I should submit a paper SA100 with 'amended' on each page to indicate the change. (If my letter had been replied to or I'd been advised correctly I could have updated the 2021-22 SA online but no longer can). Can you advise if the above is correct and if so whether the SA100, SA107 and R40 should all be sent to the Self Assessment address? If not, where should I send them?

Hi author-michael.
We do have a backlog at present.
You can get an idea of an expected date of reply by checking here:
Check when you can expect a reply from HMRC
Thank you. 
 

I'm afraid this isn't very helpful. I wrote in Sept 2023 and the tool says I should have had a reply in February 2024. It is now September 2024 and I've not even had an acknowledgement of my original letter or follow ups.