Look, I'm sure you are frustrated, but you came here for help. So stop yelling at us for every attempt we make to help you. It is extremely unpleasant.
How would I know what you have or haven't done. If, as you stated, you simply removed that old yahoo ID from your Apple Account, and replaced it with your gmail account, then of course the old yahoo ID would no longer be a valid Apple ID, and it may no longer even be a valid email address, but you seem to have missed the understanding of the situation (based on what you stated regarding the Apple ID).
An Apple account is an Apple account. You can change the email address used for that Apple ID on that Apple account whenever you want. Sometimes when people do that, they forget to sign out of iCloud (and iCloud is the only place where this is a problem).
So, they change their email address, but the old email address that used to be the ID used for that Apple account is still signed in to iCloud (drat!). A year or so ago, we had to go through some real manipulations to get things lined up so we could get that old version of the Apple ID removed from the device. But.....Apple fixed that about 6 months ago, and since then, all you have to do is sign out the old ID with the current password (because it is the same Apple Account).
Since you have finally clarified that, in fact, the old version of the Apple account ID is signed into iCloud on your device, then you now have a common problem that gets resolved daily.
If, there is other information that is not outlined here, then the diagnoses for your issue is undoubtedly quite different. However, with the information I currently have, it appears to be the everyday "I forgot to sign out of iCloud before I changed my Apple ID"....
GB