I recently changed my email address on file for every account/service. Probably 80% were straightforward to do myself, but there was a long tail of probably 10%

I recently changed my email address on file for every account/service. Probably 80% were straightforward to do myself, but there was a long tail of probably 10% where customer support had to do it for me and 10% where I was told that changing email addresses was impossible and I'd have to create a new account and submit a request to have my old one deleted.