It would had been easier if it wasn't so badly chipped away. Whilst it was rounded, you had more options to get it out.
At this point you only have 2 options.
Remove the hub then clamp it down and drill out the entire stud.
Remove the hub, grind away the backing of the stud and press/hammer out the stud.
The second is the easier option. Either way you will need to change the stud.