mercury 225HP optimax - Can't remove prop/hub

Hello,
The problem started when the motor running fine but boat won't move forward or backward. So I think it's the hub. So tried to replace the hub but no luck. I cannot unscrew to remove the prop/hub. Tried in neutral/reverse/forward. I own the boat just few months so don't have much experience. I guess I am dealing with a much bigger issue??? Any one could please give me some advise/hint for troubleshooting and how to unscrew to remove prop/hub? Any help/advise greatly appreciated.
The 25 seconds video shows how I tried to unscrew.
https://www.youtube.com/watch?v=jbtnZCJl1sY

try lifting up the tabs of the tabbed washer so they are ALL free from the grooves in the splined washer and then hit it with an impact wrench...

and it does appear the hub has spun...

makomark said:

try lifting up the tabs of the tabbed washer so they are ALL free from the grooves in the splined washer and then hit it with an impact wrench...

and it does appear the hub has spun...

Click to expand...

Thank you for quick repsond @makomark. I'll find a tool to remove the tabbed washer however the washer shouldn't have any impact on losing the bolt or am I wrong? Thanks.