Change Apple ID back

Basically it is showing the unwanted email address (under settings as the apple ID) but using the password for Apple ID I want to use (not sure how that is ever possible) and anytime I try to change the email it just says verification failed, an unknown error occured. It shows online (when I log onto the computer) that it is using the correct email (apple ID - my old one for my phone, watch, and ipad). My ipad changed back to the correct one but the iphone and apple watch still show the old ID as my apple ID but accept the password for my old apple ID.