Name not updating in parts of account

Since the name was changed three years ago, this is unlikely to be a normal synchronization delay.

First, confirm that the correct name appears on your Microsoft account at https://account.microsoft.com/profile. Microsoft explains how the account name is managed here: https://support.microsoft.com/en-us/account-billing/how-to-change-your-user-account-name

On your iPhone/iPad, sign out of your account in Word, Excel and the Microsoft 365 app, completely close the apps, then sign back in. Microsoft’s instructions are here: https://support.microsoft.com/en-us/account-billing/sign-out-of-office

If the old name still appears, go to iOS Settings > Word/Excel/PowerPoint > Reset and enable “Delete Login Credentials,” then reopen the app and sign in again. This clears the old Office account information cached on the device.

After that, create a new comment in a shared document to test it. Existing comments may still retain the author information stored when they were originally created.

Thanks for the answer and I have done all of that. In fact I have changed PC, Phone, Ipad during the 3 year period so it shouldn't be cached. When I do logout and reset and log back in again it often changes to the correct name but then a day or so later goes back to the old one. I wondered if it might be somewhere in my online profile that I need to delete/change

Thanks for confirming. Since this happens on different devices and the correct name later changes back, it is probably not a local cache issue.

If this is a personal Microsoft account and https://account.microsoft.com/profile already shows the correct name, please contact Microsoft Support at https://support.microsoft.com/contactus and mention that the name changes back automatically after about a day. This likely needs a server-side account profile check.