My mother can't access her Hotmail account anymore and retrieval attempts failed, please help

My 84 year old mother is using the same Hotmail account for around 20 years and yesterday, she suddenly got locked out of her account. She didn't see any option to sign in with her password again. Instead, she could only sign in with a code that would be sent to her phone number. However, this phone number doesn't exist anymore and she never updated it. She then tried to retrieve her account by filling in a form, but she didn't remember some of the answers she had to give, like what her first pet name was and whether she had to fill in her maiden name or not. She had given my email address as a contact address and I got an email from Microsoft, saying that she didn't provide sufficient information for her account to be restored. I then tried to help her by filling in a more elaborate form that I received, from my own phone. I had to fill in email addresses and the exact topic of the emails she had sent, but she remembered only two email addresses and only 1 topic, so I feared this wouldn't be enough. And indeed, this went wrong, because when I sent the form, there was a message that there were too many retrieval attempts and that her account is blocked now. We have no idea how to retrieve her account anymore now and she really need access again because unfortunately, all the important national organizations send her important emails there and many important documents are stored only in her email messages, because she never saved them to her files or printed them. How can we get help from a human Microsoft staff member? We're from The Netherlands.