Q: ERASE ALL CONTENT AND SETTINGS

Okay, what about it?

Are you capable of providing more than a simple statement?  Possibly explaining what the issue you are experiencing?

hooked up the 5s a couple of weeks ago and currently preparing to mail in my old phone to verison/apple to get credit for it.  i prefer to send it in after all the content is erased.  error message "internet connection is off line"

well it should be because the phone is deactivated.  how do i erase content on this old phone being offline?

Nothing about erasing or restoring an iDevice requires it to be online or even prompts for such a thing.