Has anyone experienced a unknown accounting firm to get into your Quick Books and make changes? I have this problem and QB's doesn't know who it is or how to stop it.!

Welcome to Community, @rbmattila1

I have some information about removing unauthorized users from your account. You can delete or remove users from your account so they can't access it anymore. Let's go to the manage user screen to do it.

1. Go to the Gear icon at the top.
2. Select Manage users.
3. Tap the Accounting firms tab. Verify the accountant in question from the list.
4. If found, click Delete.

You can refer to this article for more information: Add an accountant to review your accounting in QuickBooks Online.

Additionally, make sure there are no unauthorized users listed to log in to your account. If the firm is not on the list of accounting firm, you'll want to contact our Customer Care Support so we can assist you further. They have a special tool that can remove users too.

Here's how to reach them:

1. Go to Help at the top.
2. Scroll down and keep typing I still need a human until you reach the option to connect to one of our live support agents.
3. Click Get help from a human.
4. Choose either Chat with us or Have us call you.

In case you need help with other tasks in QBO, feel fee to browse this link here to go to our general topic with article. 

Let me know if you still have questions or concerns with managing account users. I'll be around to help. Have a wonderful day ahead.