Catch-22 with Common Reporting Standard and NI Numbers

Hi, I am attempting to change some details on a Mauritian bank account I own. However, I’ve been informed that I must now give my UK address and UK National Insurance number as that is where I reside most of the time. They did not inform me of why, but it appears this is due to the Common Reporting Standard. Unfortunately, while I live in the UK for most of the time, I do not have a National Insurance number there as I a) Have not worked and will not work in the UK b) Have not claimed and will not claim benefits in the UK c) Am not eligible for state pension As such, I am not eligible to receive an NI number. This is now blocking me from doing anything with my Mauritian account and I’ve told it’ll be blocked until I update them with this info. Please can you advise me on what my next steps are? Many thanks.

Hi,
To obtain a National Insurance (NI) Number you must have a reason:
Employment including self employed 
Claiming benefits or UK State Pension
As you have already advised you do not do either of these things, then there is no reason for you to obtain a UK NI number. NI numbers are a unique reference for an individual to pay UK tax and National Insurance.
Unfortunately there isn’t anything further we can advise, you will have to confirm this with your bank.
Thank you.