I called this Tuesday to confirm that the invoice and time sheet I sent on Monday had arrived. What a surprise, no they hadn't. I sent them again, to the same guy as I'd sent the previous week's. I checked again yesterday and the first of these invoices hasn't been processed and he didn't remember receiving them. After much rooting about he found them and promised that they would be processed this week.
What's most annoying about all of this is that it always happens at month ends when I can least afford not to be paid. I pity the contractors that bill monthly.