When was the last time you accessed your account?
If you haven't signed in for the last 270 days, your account has been marked as inactive.
Please be informed that free Windows Live Hotmail accounts become inactive if you don't sign in for more than 270 days or within the first 10 days after signing up for an account.
After an account becomes inactive, all messages, folders, and contacts are deleted.
Incoming messages will be sent back to the sender as undeliverable.
Your account name is still reserved. However, if the account stays inactive for an additional 90 days, the account name may be permanently deleted. If you don't use your Windows Live ID for 365 days, your Windows Live ID may be permanently deleted.
I believe you can provide the affected email address on a private thread so the "powers that be" can investigate the account on their end.
Were you aware that Hotmail is currently upgrading to Outlook.com?
Is it just possible your Hotmail account is now an Outlook.com account?