Seeking Solution

I have been trying to pay Voluntary NI contributions for more than 18 months. I originally applied in December 2022 to pay Class 2 voluntary NI contributions as I have been working overseas for many years. That application was processed, however, I was informed that I needed to resubmit the application, requesting Class 3 voluntary contributions instead. My new application for Class 3 contributions was submitted in August 2023 and was marked as Complete on my portal in March or April 2024. Whilst on vacation in the UK in June, I phoned the HMRC helpline to follow up on this application and was assured a shortfall letter informing me how to make payment would be sent shortly. I have still not received a shortfall letter and am therefore unable to make payment. How long does a letter normally take to process? Should I follow up again via the helpline or is there simply a backlog with processing shortfall letters?

How long should it take to get a response after registering for the first time for self-assessment? After many years of working overseas, I registered for the first time - online - for self-assessment a few months ago, but have heard nothing back. This is to pay some tax on savings for last year. How long should I expect before receiving notification from HMRC that I am registered?