Error when trying to log in to an old account.

My SO has been locked out of Instagram and her reset password email was sent to an old Hotmail account. When trying to log into said Hotmail account, it says "That Microsoft account does not exist.". We have tried to reset password on that account but due to it being non-existent, it didn't work. I red somewhere that after inactivity of 365 days, a Hotmail account would be deleted. Is there a way to retrieve that email?

Thinking that if it was deleted and the email account was sent back into the system (For re-use I assume), I then tried to create a new email using the same account name. I then got this error saying "This email address is part of a reserved domain such as live.com, hotmail.com, or msn.com. Please enter a different email address.".

I can't reset the email of the Instagram account without logging in and when looking for help there they told me to contact Microsoft.

Is there any solution to this problem?

Thank you.
Danny.