2004 ballasts replaced, all good til headlight went out

A month ago I replaced both the ballasts on my 2004 Prius using aftermarket ones off Amazon. All was good, and the intermittent problem of a headlight going out was solved. But now just the driver's side bulb is out for real --- no longer 'fixed' by turning the lights on and off. So I replaced it with a Philips D2R C1 as per what seemed like the right one on Amazon for $55.78, but it's still not working. What did I do wrong?