Old Apple ID will not stop popping up

I have an Iphone 6 Plus and running IOS 11.0.3. I have updated Itunes to version 12.7.1. Ever since I updated to IOS 11, an old APPLE ID keeps popping up on my phone screen. It's an old work email so it doesn't exist anymore. I think some of my old songs and/or apps that synced when I did the IOS update must have been purchased under that old Apple ID. I have read some articles and community posts and here is what I have tried:

• One post said to open Itunes, right click on the song or app in question, click "file" and it will tell you what ID it was purchased under. One I identify it, I can delete the old song or app. Since the IOS update now does not allow apps to sync with Itunes and the entire "APPS" tab is gone from Itunes - what is the work around?
• Right clicking on a song doesn't work either. There is an option called "Song Info", then I can click on a file tab, but it won't show me the Apple ID that used either.
• I even talked my old boss in to re-activating my old email address temporarily even though I haven't worked there in 8 years. I re-set up that Apple ID online, new password, tried logging in to it on my phone with the Apple ID prompt pops up - and it says it's invalid still.
• Called Apple Support -they show no record of that old Apple ID ever existing. Wiped/cleared phone, restored from backup - old APPLE ID still popping up because somehow, my Icloud is signed in to the old ID and my Itunes (on my phone ) is signed in to my new/correct Apple Id.
• I do have a proof of purchase but Apple Store won't help with software issues anymore, only hardware issues. I've talked to Apple support 3 times now with this same problem and most of these solutions I've tried have come from articles and this community. All they have ever had me do is wipe it clean again and restore from backup to no avail.