Why is my character controller deacceleration not working?

I want my player to deaccelerate when he stop not just stop in place. Here is my code:

public override Vector3 Move(MovementManager manager, Vector2 input, bool jump, bool isCrouching)
{
    float speed = isCrouching ? CrouchSpeed : MoveSpeed;
    Vector3 velocity = manager.Velocity;

    float currentVelocity = new Vector3(velocity.x, 0, velocity.z).magnitude;
    Vector3 moveDirection = Vector3.zero;

    if (Mathf.Abs(input.x) > 0 || Mathf.Abs(input.y) > 0)
    {
        moveDirection = new Vector3(input.x, 0, input.y);
        moveDirection = manager.transform.TransformDirection(moveDirection);

        if(input.y > 0)
        moveDirection *= input.y;

        LastMoveDirection = moveDirection;

        if (IsWalkSpeed) currentVelocity += (Acceleration * .4f) * Time.fixedDeltaTime;
        else currentVelocity += Acceleration * Time.fixedDeltaTime;

        //if (currentVelocity > MaxSpeed) currentVelocity = MaxSpeed;
        if (currentVelocity > speed) currentVelocity = speed;
        return moveDirection.normalized * currentVelocity * Time.fixedDeltaTime;
    }
    else
    {
        currentVelocity -= Deacceleration * Time.fixedDeltaTime;
        currentVelocity = Mathf.Max(currentVelocity, 0);

        return LastMoveDirection.normalized * currentVelocity * Time.fixedDeltaTime;
    }
}