Player prefs

I'm using playerprefs to store the coins collected during the current level and it add it to the previously collected coins. The problem is when i go to the shop menu my coins are getting doubled like i have earned 50 coins during the current level then in the shop the total coins is 100 whereas the total coins should be 50. And when i close the game my total coins in the menu gets replaced with the one's in the shop.

Here's my save system script:-

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 using TMPro;
 public class SaveSystem : MonoBehaviour
 {
     public TextMeshProUGUI menu;
      int total;
     
     
     // Start is called before the first frame update
     void Start()
     {
         total += PlayerPrefs.GetInt("coins") + Score.score;
         menu.text = "  : " + total.ToString();
         save();
     }
 
 
     public void nextLevel()
     {
         save();
         SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
         Time.timeScale = 1f;
         Score.score = 0;
     }
 
     public void mainMenu()
     {
         SceneManager.LoadScene("MainMenu");
         Time.timeScale = 1f;
     }
 
     public void resetGame()
     {
         PlayerPrefs.DeleteKey("coins");
         SceneManager.LoadScene("MainMenu");
     }
     public void save()
     {
         PlayerPrefs.SetInt("coins", total);
         PlayerPrefs.Save();
     }
 }

And my shop script is :-

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using TMPro;
 public class ShopSystem : MonoBehaviour
 {
     public GameObject btn2, btn3, btn4, btn5;
     public Button skin1, skin2, skin3, skin4, skin5;
     bool skinBought2, skinBought3, skinBought4, skinBought5;
     //public float errorMessage = 3f;
     public TextMeshProUGUI insufficientFunds;
     int coins;
     public TextMeshProUGUI buyText;
     public void Start()
     {
         coins = PlayerPrefs.GetInt("coins");
          skin1.interactable = true;
          skin2.interactable = false;
          skin3.interactable = false;
          skin4.interactable = false;
          skin5.interactable = false;
         insufficientFunds.enabled = false;
     }
 
     void noFunds()
     {
         insufficientFunds.enabled = false;
     }
 
     public void Buy2()
     {
         if ( coins >= 120)
         {
             Destroy(btn2);
             skin2.interactable = true;
             coins -= 120;
             buyText.text = coins.ToString();
             PlayerPrefs.SetInt("coins", coins);
             PlayerPrefs.Save();
         }
         else
         {
             insufficientFunds.enabled = true;
             Invoke("noFunds", 3f);
             
         }
     }
 
     public void Buy3()
     {
         if(coins >= 220)
         {
             Destroy(btn3);
             skin3.interactable = true;
             coins -= 220;
             buyText.text = coins.ToString();
             PlayerPrefs.SetInt("coins", coins);
             PlayerPrefs.Save();
         }
         else
         {
             insufficientFunds.enabled = true;
             Invoke("noFunds", 3f);
             //Debug.Log("Insufficient funds!");
         }
 
     }
 
     public void Buy4()
     {
         if(coins >= 320)
         {
             Destroy(btn4);
             skin4.interactable = true;
             coins -= 320;
             buyText.text = coins.ToString();
             PlayerPrefs.SetInt("coins", coins);
             PlayerPrefs.Save();
         }
         else 
         {
             insufficientFunds.enabled = true;
             Invoke("noFunds", 3f);
             //Debug.Log("Insufficient Funds");
         }
     }
 
     public void Buy5()
     {
         if(coins >= 420)
         {
             Destroy(btn5);
             skin5.interactable = true;
             coins -= 420;
             buyText.text = coins.ToString();
             PlayerPrefs.SetInt("coins", coins);
             PlayerPrefs.Save();
         }
         else
         {
             insufficientFunds.enabled = true;
             Invoke("noFunds", 3f);
             //Debug.Log("Insufficient Funds");
         }
     }
 
 
 }