Change of Address so difficult

I have previously struggled to change my address with Computershare and after much frustration, some of my accounts have been updated, yet not all of them. I recently called them to update 1 of my accounts that was not updated, and they want me to go through the whole procedure again of sending documents via registered mail - they won't accept an email and neither are they able to trace the previous documentation I sent them. This is in spite of them having my new address for other accounts of mine. So they are happy to continue sending mail to an invalid address, unless I redo the paperwork, which is rather onerous considering only 3 digits in my PO Box number need to be changed. When I asked to speak to the supervisor, I was told that the supervisor would tell me the same thing, So frustrating! Life is too short to be bothered with all these rules and procedures - especially to have to redo them through no fault of my own.