How do I cancel a sales order after invoiced

This is a service business. We don't use jobs, instead, we use sales orders and non-inventory items. When we book a sale we create the sales order and create invoices with due dates on the dates that we anticipate completing portions of the work. This gives us a good look at our cash flow based on receivables. We actually bill the customers credit card on the invoice due dates, assuming we have completed our work, as per contract.

However, it is not uncommon for a customer to cancel before we collect their deposit, and after we have set up the sales order and invoices.