A law firm did a lot of work for my company. He sent us a first invoice and we paid it. Nine months later, he told us that he forgot to bill us for some of the work that he did for us and he sent us a second invoice.
Let's assume for the purposes of this question that he did all the work described in the two invoices and that the work was satisfactory.
We are annoyed to receive a second invoice nine months late. We already closed the books for last year and it messes up our budgeting.
Do we have a legal basis for not paying or asking for a discount for the second invoice?