About 2 almost 3 years ago I purchased an iPod touch 5. My phone and my iPod both have 2 different Apple ID's (same as 2 different email addresses). The email address used for my iPod is an email I no longer use and I'm not sure if I deactivated it or not. Anyway when I go to Settings> iCloud> it still tells me that same old email address.
Sign in with your old Apple ID at iCloud.com, go to Settings->Manage (Apple ID)->Click on your iPod and remove it from the list of devices. And finally use your new Apple ID on your iPod.
Contact apple directly, only they can authorise Apple ID merges or the transfer of products from one ID to another.
Use the link below to get the details. I would have my passport/ID at hand, you may also have to send them a scan of proof of purchase or proof of identity.