Apple ID change

I

iMore Question

So i Read this guide --> https://www.imore.com/how-change-email-address-associated-your-apple-id
And it didn't help. Somehow after I changed email address on the AppleID that iI didn't use and replaced it with a new email I created, I still couldn't change to desired email on my current AppleID. It says that that email address is unavailable!
Please for your help as soon as possible!
Thanks in advance