Why does music that I deleted off my phone still play when I plug it in to the usb?

Here's a good one for you guys. I have an HTC hero, i loaded it with some music, plugged it in via usb in our 2009 scion xb and it worked. But now, i have since deleted that music and put different songs on, but for some reason the car doesn't recognize the new music and still plays the old stuff, and its a lot. Why is it playing the same list and how can I change it? Is it the car or my phone? I deleted all the music on my phone and the car still plays the original list. Is it in the cars memory or something and how can i fix it.