What they've told is correct, as far as it goes. If the music on your iPod came from someone else, then you have no right to keep it or make a copy into your iTunes Library. That isn't something Apple made up, it's how the music industry works (it's the same with written works [books] etc.).
So the big question is: where did the music on your iPod come from? If it is yours (in other words, you paid a legitimate source for it), then the next question is; is it in your iTunes Library? If it is, copy from that library onto your phone. If you no longer have that library, did you make a backup that you could use? If not, then you will have to obtain the music from the source you obtained it from in the first place:
- from a CD (compact disc) that you purchased, use iTunes to make a new copy into your current iTunes Library
- online purchases from the iTunes Store - log into your iTunes Store account and look for your purchases under your account detail. Then download them again
- online purchases from Amazon, Bandcamp etc. - sign in to your account with that outlet and look for under your account for your purchases and download them again
- other online sources, such as an artist's website - return to that site and hope that you can download them again