One time purchase

I have something that really annoys me and I hope some of you could help me with it. I have been using Player Prefs and so far as far as customisation purchasing is concerned it has worked very well. However, when I have attempted to use this with a game mode for purchase. Every time I press the button it decreases my coins (my micro transaction system). I would like it to make a one time purchase. Thanks in advance. Here is my code:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CustomisePayment : MonoBehaviour {
	private int CoinCounter;
	private string PrefPurchaseHoleInAWall;
	// Use this for initialization
	void Start () {
		PlayerPrefs.SetString ("PrefPurchaseGameMode",PrefPurchaseHoleInAWall);
		CoinCounter = PlayerPrefs.GetInt ("CoinCount",CoinCounter);
		if (PlayerPrefs.GetString ("PrefPurchaseGameMode", PrefPurchaseHoleInAWall) == "PurchasedGameMode") {
			PrefPurchaseHoleInAWall = "PurchasedGameMode";
			PlayerPrefs.SetString ("PrefPurchaseGameMode", PrefPurchaseHoleInAWall);

		} else {


			PlayerPrefs.SetString ("PrefPurchaseGameMode",PrefPurchaseHoleInAWall);

	// Update is called once per frame
	void Update () {
	public void OnPressPurchaseHoleInWall(){
		if (PlayerPrefs.GetString ("PrefPurchaseGameMode",PrefPurchaseHoleInAWall) != "PurchasedGameMode") {
			if (CoinCounter >= 300) {
				CoinCounter -= 300;
				PlayerPrefs.SetInt ("CoinCount", CoinCounter);
				PrefPurchaseHoleInAWall = "PurchasedGameMode";
				PlayerPrefs.SetString ("PrefPurchaseGameMode",PrefPurchaseHoleInAWall);
				Debug.Log ("Purchased");
		if (PlayerPrefs.GetString ("PrefPurchaseGameMode",PrefPurchaseHoleInAWall) == "PurchasedRed") {
			Debug.Log ("Not Purchased");


You are using PlayerPrefs in a wrong way.

PlayerPref items have exactly one key and one value.

// Loading
var number = PlayerPrefs.GetInt("My Number");

// Saving
PlayerPrefs.SetInt("My Number", number);

However, in your code, you seem to try to add multiple keys in order to create some sort of hierarchy - PlayerPrefs doesn’t have that.

PlayerPrefs.GetString ("PrefPurchaseGameMode", PrefPurchaseHoleInAWall)

Instead, the second parameter is a default value that gets returned by the Get functions in case there is no value found for that key.

If you want to combine strings to create keys, you can use string concatenation:

PlayerPrefs.GetString("PrefPurchaseGameMode" + PrefPurchaseHoleInAWall)