Hello,
This is one of a few problems common to using ISP email addresses and free email addresses.
There is limited support for free email addresses. ISP email addresses are not portable if you change ISP's.
In this case, it appears to have an ISP address associated with a business internet account.
The best you can do is ask you previous employeer to recreate the address and have the emails forwarded to your new email address.
They may be nice and allow it for a couple months. Keep in mind they might recreate it as a copy+forward and monitor the email passing through it to protect their business.
If you want an email address with better support that can follow you for life I recommend that you
register your own domain name.