Hi karlm01,
Thank you for posting to Apple Support Communities.
We’ll need some additional information to provide more specific support.
When you attempt to add the email address back again, are you using the Other option? This gives you the option to manually enter in the server information. Try this option and use the configurations for your email address from here: Mail - Official Apple Support
Are you seeing a specific error about your user name? If so, you'll need to contact Charter for help with this. You can use the steps below for more options:
Contact your email provider or system administrator
1. Contact your email provider or check their status webpage to see if there's a service outage.
2. Ask your email provider or system administrator if you turned on any security features or restrictions, like two-step verification, for your email account. You might need a special password or might need to request authorization from your email provider to send and receive email on your device.
3. Check your email account settings with your email provider or system administrator to make sure that they're correct.
This information is from If you can’t send email on your iPhone or iPad - Apple Support.
Take care.