How to Permanently Delete a Customer
Log in to the Panel and go to Customer Manager > Customers
Find the partner that you need to delete > click on Options (three vertical lines):
You'll get a warning now about provisioned services. If you see any active services listed here, double-check now if you really want to delete this particular customer!
If you're absolutely sure, click OK.
Then tick in the Show Deleted check box and look for the customer again:
Now, the only option in the menu will be "Permanent delete". Click on it and the customer will be permanently removed with all its billing data from the Machpanel database.