Unrecognized ID

I have a friend that has a 6 plus phone running 11.2 and an older iPad Running the same. Both are registered with the same Apple ID. When she attempted to make a purchase in the App store and entered her password it was rejected. After repeated attempts no love. I sat with her as we navigated to the Apple ID web page, entered her ID and hit the link to change her password and surprisIng got the message that this ID does not exist. I checked both devices and yes they both we are registered under the same ID. She also pays for icloud storage (50 gb) of which 20 gb is used. The devices backup daily. To be clear, the id is not disabled. ” lt does not exist”. I’m out of ideas how to rectify this situation.