Why is my pause menu script only working once? SetActive only working with false

I'm wondering why my pause script doesn't work as expected. It should freeze the time and bring up the Pause menu, but instead it only freezes and nothing happens after that. And i can't resume the game too

using System.Collections;
using System.Collections.Generic;
using System.Threading;
using UnityEngine;

public class PauseMenu : MonoBehaviour
{
    // Start is called before the first frame update
    public static bool GameIsPaused = false;
    public GameObject pauseMenuUI;



// Update is called once per frame
void Update()
{
    if (Input.GetKeyDown(KeyCode.Escape))
    {
        if (GameIsPaused)
        {
            Resume();
        }

        else
        {
            Pause();
        }
    }
}

void Resume()
{
    pauseMenuUI.SetActive(false);
    Time.timeScale = 1f;
    GameIsPaused = false;
}

void Pause()
{
    pauseMenuUI.SetActive(true);
    Time.timeScale = 0f;
    GameIsPaused = true;
}

}