2000 V6 belt tensioner !@#$%$#@#$
 

I am trying to change the belt tensioner on my 2000 honda accord V6. It is for the alternator. The pulley is off and the two bolts are out but the star nut in the middle is impossible to get off. I tried a 23 mm socket but it didnt work and no one in the state of NJ seems to know what I am talking about when I ask about this situation. Maybe someone can be of some help.