Account transfer / Verification email

Three months ago I acquired a Amazon UK brand. Transfer was very smooth and previous owner and myself are on good terms and text each other almost every day.

However, for some reason the primary email in the Account info/business information/identity information is still previous owners email, nobody knows why.

This means that although I have access to most parts of the seller central I can not update certain things, amazon emails go to previous owners and an agency I hired can't access information, same goes for my accountant because I can't invite and confirm.....

Over the last 3 months I have spoken on the phone with one person from Amazon, that was in mid January, that person has since vanished and ive emailed with about 5-6 different people from Amazon - email is always the same "we understand, we are working on it and we will get back to you"

Anyone has any kind of tips how to move this forward ?

Thank you.