This tends to happen for a few users, if it happens to you please follow the below to remove the icon:
1. On your iPhone select settings -> phone -> call forwarding
2. Swipe from OFF to ON
3. Select forward to and enter your HulloMail box number.
4. Swipe from ON to OFF
The icon should now disappear, if you an unaware of your HulloMail box number please email email@example.com and we can advise you what it is.