Eliminating an old apple ID

This is my first ever post and my name says it all! 🙂 My 6 SE still thinks that my apple ID = my old email address. I switched from a comcast email to an att email address over two years ago not knowing the trouble that would ensue. I've establish a new apple ID and PW via the apple website using my att email address, but my 6 SE continues to ask for my old PW that was connected to my comcast apple ID. I don't even remember that PW and don't think it really matters anymore. I went through a multitude of email exchanges with apple support, but that was over a year ago. It strikes me that the fix for this should be easier than it seems to be. I thought I'd reach out to this community for help of which any is much appreciated! 🙂

Thanks so much!!!