I changed my apple id months ago and all of a sudden i've been getting pop ups on my iphone for confirmation of my old apple id which no longer even exists, my iphone won't even allow me to use my new apple id to update or upload anything.

I changed my apple id months ago and all of a sudden I've been getting pop ups on my iphone for confirmation of my old apple id which no longer even exists, my iphone won't even allow me to use my new apple id to update or upload anything. This has honestly become an on going nuisance and I've recently updated my iphone to ios 9.3 and I can't even get into my phone because it requests my old apple id which does not even exist, please help someone.