All songs deleted from ipod when plugging it into another itunes

Okay, so I recently bought a second hand ipod classic from Ebay and it came preloaded with around 4500 songs on it. I plugged it into my computer (windows) hoping to add my current music library to it. However, after a few problems getting itunes to recognise it, it gave me the option to sync which it said would delete all the music on the ipod. I obviously didn't sync as I didn't want to lose 4500 songs. I then searched a bit looking for how to have both libraries on the ipod and got the impression that I needed to manually manage the music on the ipod (maybe this wasn't right?? I really should have been more careful). After ticking the box for manually managing music it made me eject the ipod and I did so. However, I looked on the ipod right after ejecting and there was nothing there; it had been entirely wiped clean. I plugged it back into the computer in a panic (also something I should have waited before doing) and its now on my itunes but completely empty, without even the name of the previous owner anywhere on itunes or the ipod. Can anyone help? I would really really like to get the music back although I fear that might be impossible unless I send the ipod back the the Ebay seller to get synced again, which I don't want to do as the music was a bonus and I didn't pay much for it anyway.

Can anyone help?