JS to C#, anyone?

Thiiiis should work, might have a few minor bugs. But honestly, I only did this because I had nothing better to do. If it doesn't work, spend time fixing it to work before going any further with C#. That's how you learn, fix stuff up.

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class BallCollide : MonoBehavior
 {
     public Collider colliding;
     public RigidBody body;
     public float forceMultiplier = 25;
      
     public void OnCollisionEnter(Collision collisionInfo) 
     {
         if (collisionInfo.gameObject.name == "Ball")
         {
             string contactNormal = collisionInfo.contacts[0];
             Quaternion rot = Quaternion.FromToRotation(Vector3.up, contactNormal.normal);
             // This might supposed to be something else, but I'm guessing it's a Quaternion.
             float pos = contactNormal.point;
             var rv = collisionInfo.relativeVelocity.magnitude;
             // I have no idea what this is supposed to be, which I'm kicking myself for.
             var direction = body.transform.position - pos;
              // Again, no idea. Might be a float[]
              
             Vector3 reflectBallTo = Vector3.Reflect (pos, direction);
              
             colliding.gameObject.rigidbody.AddForce (reflectBallTo * forceMultiplier);
         }
     }
 }