I am trying to understand how the NEW invoices are charged to customer.
I know that the Softlayer portal lets us download the LAST RECURRING INVOICE, which should be the final bill for the previous billing cycle. My question is what happens to the NEW invoices that were generated for the last billing cycle? Does the customer pay the sum of the LAST RECURRING INVOICE and NEW INVOICES ?
Yes, the customer pays the NEW Invoices for the new service, this adds to the balance in the last billing cycle.
The "NEW" signifies an invoice for new service and this invoice amount add to balance.
You could review the invoices category type in the next link: https://sldn.softlayer.com/reference/datatypes/SoftLayer_Billing_Invoice/#typeCode