It seems like the issue might be related to the fact that you are defining user_instance as a global variable. Since the bot might be handling multiple requests concurrently, using a global variable for user instances might lead to unexpected behavior, especially in a multi-user environment.

To fix this issue, you should avoid using a global variable for user_instance and instead create an instance for each user separately. You can maintain a dictionary to keep track of user instances using their IDs.

Here’s a modified version of your code:

from discord.ext import commands
from discord import Intents
import datetime
import discord

intents = discord.Intents.all()
intents.message_content = True

bot = commands.Bot(intents=intents, command_prefix="!", case_insensitive=True)

user_instances = {}

class User:
    def __init__(self, user):
        self.user = user
        self.points = 0

    async def play(self, ctx, number):
        # Your play logic here
        pass

    async def point(self, ctx):
        # Your point logic here
        pass

@bot.command(name="register", description="Register a User")
async def register(ctx):
    try:
        await ctx.send("Getting you registered...")
        user = ctx.author
        user_instances[user.id] = User(user)
        with open("user.txt", "a") as file:
            file.write(str(user) + "\n")
    except discord.HTTPException as e:
        await ctx.send("Oops! There was a problem Registering you. Speak with your admin.")

@bot.command(name="play", description="Playing the Guessing Game")
async def play(ctx, number):
    user = user_instances.get(ctx.author.id)
    if user is not None:
        await user.play(ctx, number)
    else:
        await ctx.send("Please register first using !register.")

@bot.command(name="points", description="Amount of points user has")
async def points(ctx):
    user = user_instances.get(ctx.author.id)
    if user is not None:
        await user.point(ctx)
    else:
        await ctx.send("Please register first using !register.")

if __name__ == "__main__":
    bot.run("YOUR_BOT_TOKEN")

In this modification, each user has a separate instance of the User class, and the instances are stored in the user_instances dictionary using the user ID as the key. This should prevent the issues with multiple users and repeated messages.