Hello there! Follow the steps below.
log in with your apple id on your computer under "manage you apple id"
copy the link below and select manage id.
. When your logged in click at "edit" after "Apple ID and primary email address". Change your email address (if you don´t have another email address, you have to get one). When you have changed your email address you will receive a confirmation email to the your new email address, click on the link "confirm now" in the email. After this step, log out from your account and then log in again to make sure that i works. Next step is to go to www.icloud
.com, and try your new account there as well, if it works you can log out.
If everything works this far it's a good sign. Next step is to log in your apple id account on your computer and change back to the email you had before the change, confirm the email you will receive. Log out from your account and log in again to make sure that it works. After this step enter your apple id och password ***** your iphone and see if it works.
If this doesn't work you have to do a factory reset too and after this it will definetly work