How come my the y velocity does not change in the script.

The problem is as you can see below is that when the ball touches a wall it does not bounce as i want it. https://gfycat.com/ShadyPortlyBug

This is the script for bouncing.

  void OnCollisionEnter2D(Collision2D coll)
     {
             Debug.Log(GetComponent<Rigidbody2D>().velocity.y);
 
         var newPS = Instantiate(ballhit, transform.position, transform.rotation) as ParticleSystem;
 
         newPS.startColor = coll.gameObject.GetComponent<SpriteRenderer>().color * GetComponent<SpriteRenderer>().color * 0.5f;
 
         if (coll.gameObject.tag == "Walls")
         {
             var rb2d = GetComponent<Rigidbody2D>();
             rb2d.velocity = new Vector2(rb2d.velocity.x , rb2d.velocity.y * -1);
             
 
         }
         if (coll.gameObject.tag == "Paddle" && directionRight == currentDirection)
         {
             LeftDir();
         }
         else if (coll.gameObject.tag == "Paddle" && directionLeft == currentDirection)
         {
             RightDir();
         }
             //BallsMovement based on the paddles y position.
             if (coll.gameObject.name == "LeftPaddle")
             {
            GetComponent<SpriteRenderer>().color = coll.gameObject.GetComponent<SpriteRenderer>().color;
             float y = hitFactor(transform.position,
                                     coll.transform.position,
                                     coll.collider.bounds.size.y);
 
                 // Calculate direction, make length=1 via .normalized
                 Vector2 dir = new Vector2(1, y).normalized;
 
                 // Set Velocity with dir * speed
                 GetComponent<Rigidbody2D>().velocity = dir * speed;
 
         }
           
         if (coll.gameObject.name == "RightPaddle")
         {
 
            GetComponent<SpriteRenderer>().color = coll.gameObject.GetComponent<SpriteRenderer>().color;
             // Calculate hit Factor
             float y = hitFactor(transform.position,
                                 coll.transform.position,
                                 coll.collider.bounds.size.y);
 
             // Calculate direction, make length=1 via .normalized
             Vector2 dir = new Vector2(-1, y).normalized;
 
             // Set Velocity with dir * speed
             GetComponent<Rigidbody2D>().velocity = dir * speed;
 
 
         }
     }

I would really appreciate a tip or explanation