Orange is now branded as EE so it is not a case of the email disappearing, just the server address where you store your email being changed. Contact your service provider to get the correct email address for the new email server address. It is probably just changed from
https://mail.orange.your-details, to
https://mail.ee.your-details, or something similar. There may be other settings you need to change, but essentially your email should carry on working just as it did before provided you have the correct mail server address set up in your email program/settings.
There should also be details available on the Internet available through either the Orange or EE home pages.