Lost apple ID

I've been using this ID for years. Last week it disappears, literally disappears. When I try to log into the system, it tells me that my password is incorrect, so I go to reset, where the system then tells me, that the Apple ID is not valid or is not supported. So what happened? I get on the horn with Apple support and they tell me it doesn't show up in the system. Okay, why doesn't it? In my case, I can go to the apple site and create another ID using the same email address, but I can't get the old ID off my devices. I have been working with an apple senior advisor for more than a week and still, the problem persists. Worked with a new senior advisor today, he had me restore my ipad. Now it is locked to my old ID which no longer exists.