Can't adding Force to move ball Left or Right

I am making a game where a ball moves forward in constant speed and I want to add force to move the ball left or right. But my unity is not adding force after using the AddForce function also Its not showing any arror. Here is my code

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ballMove : MonoBehaviour {
 
     Rigidbody ballRigidbody;
 
     // Use this for initialization
     void Start () {
         ballRigidbody = GetComponent<Rigidbody> ();
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         ballRigidbody.velocity =  (Vector3.forward * 20);
 
         if (Input.GetKeyDown (KeyCode.A)) {
             ballRigidbody.AddForce (Vector3.left * Time.deltaTime * 10f);
         }
         if (Input.GetKeyDown (KeyCode.D)) {
             ballRigidbody.AddForce (Vector3.left * Time.deltaTime * 10f);
         }
     }
 
 }

Why its not working?