Match3 - OnCollissionEnter problem

I’m making a Match3 game where 3 balls of same color to collide so that they are destroyed. Currently, I’m facing following problem.

When OnCollisionEnter event occurs, i’m getting component of the other game object and incrementing contact(BallCount) count. But, even for a single contact, the counter is raising to 3 and is destroying objects. Following is my code. Can somebody look in and help me ?

As per documentation, OnCollisionEnter doesnt seem to trigger every frame. If this is the case, please also tell me which is the best place for this function.

void OnCollisionEnter(Collision collision)
{

	GameObject obj = collision.gameObject ;
	obj.GetComponent<Match3>().BallCount++ ;	
		if( obj.GetComponent<Match3>().BallCount >2)
				{
					Destroy(Obj);
				}

}

OnCollisionEnter is good place for the code

add rigidbody to ball gameobjects & in the collision detection option
select continiuous but if the balls are moving very fast select the continuous dynamic