Activation Lock help

I have an older iPod. I purchased it used. It was reset by the owner and I used my Apple ID on it for a year or more. It updated and reverted to the original owner's ID and was locked. I can not access it with my account now. The original owner said they do not remember the Id or password they used to set it up. I made purchases through iTunes for music while using it. It does not show any devices on my account.