Score system not working after the score is 1

Hi all. When you kill an enemy, score must increase 1 point. It works at first enemy but when you kill other enemies it just stays at 1. Enemies spawn periodically. How can I solve it?`

public class Zombie : MonoBehaviour
  {

    int score = 0;

    private bool isDead = false;

    public Text ScoreText;

    public void TakeDamage(int amount)
    {
        health -= amount;
        if (health <= 0)
            isDead = true;

        Die();
    }
 private void OnTriggerEnter2D(Collider2D collision)
    {
        if (collision.transform.tag == "Bullet")
        {
            TakeDamage(30);
        }
    }
private void Die()
    {
        if (isDead)
        {
            score++;
            ScoreText.text = "" + score;
            Debug.Log("SKOR: " + score);
            isDead = false;
            Destroy(gameObject);
        }
    }
 }

`

Is that script attached to enemy gameobject?

If that is the case you have separate score counter for each enemy.
Your ScoreText seems to be “global” in scene so you may try to convert text to int increment it by 1 and set new value as text.