You should not necessarily expect responses from the /Calls API to match invoices, there are a number of reasons for this discrepancy.
In order of frequency of occurrence:
DELETE
method after which they will be removed from logsFor reconciling usage with invoices we provide a Usage API. The Usage API is tightly integrated with our billing platform and is able to provide counts and costs for usage even after the underlying resource has been deleted or released. Voice product usage including count is available in multiple categories, so make sure you are familiar with all the features your application uses and that you are requesting results from those categories.