I rounded it off using a closed 23mm wrench. Wouldn't budge using vice grips.

Bringing her in...

 

Pretty much, you'll need to grind off the round and see if u can go one size lower. Try to get the biggest wrench you can get, and hit it with a rubber mallet.

 

Don't use rubber mallet's buddy. You will be so frustrated with the waste of effort. Metal sledge for all work that's not a body panel. Take a picture of it for us. I'd say vice grips, but I bet it's rounded and just slips off now with a pair of vice grips. In that case, I'd be busting out my welding machine, but not all of us have access to them. Sorry, lesson learned right. ;-)