Re: I just found out my accountant accidentally has been billing people from my business account ...
If this happens to me, I would really replace my accountant.
You can talk to your accountant about it and warn your customers as well. You can also remove him from your user's list, so he won't have access to your company data. If he pays for your QuickBooks, you can ask him to detach your account from their subscription and you can pay for it.
Click the Gear icon and choose Manage users.
Go to Accounting firms tab, then find the accountant you wish to remove.
From the Action drop-down, choose Delete.
Select Delete to confirm.
Please let me know if there's anything that I can help.